PARTS
Hard Drive
If you are looking for an upgrade, I suggest looking for a 40Gb+ for the best price to size ratio as of  now It's been reported drive up to 80Gb can be used in Trasnote without any problems. I found that the cheapest source for hard drive is, interesting enough, from Dell!! Since these drives are universal, and there had been no size limitations reported, as long as you get a 9.5mm drive that fits physically, it will work. I do suggest going for the faster RPM drive if you have a little more to spend as you will see a difference for sure.
Batteries
Main battery:
Marketing P/N:  02K6713
Replacement P/N: 02K6686
    The replacement Li-ion batteries for notebook computers are always very pricy and hard to find. If you really need one, eBay is probably the best place to find it for cheap. Don't buy it unless is new. After running 180+ cycles, my battery is about 60% now no matter how many times I recondition it. Remember, you can always check how much the battery had been used by looking at the "Battery Information" in the "Battery MaxiMiser". The number of discharge cycles is saved in the battery. Here are a few sources of new and OEM batteries:OEM, from Directron ($131- Jul 22, 04) OEM from FEDCO ($149- Jan 05)

Factory battery from SparePartsWarehouse ($113 - Jan 05), Indexcomputer ($109 - Jan 05)

Direct from IBM ($169 - Jan 31, 04) <-no longer available

Sub battery: P/N 02K6684 and backup battery: P/N 02K6686     Strange things happen when these batteries run out. See Tricks and tips section for some symptoms that had been reported. These batteries are not sold online, after searching, I also found it for sale in SparePartsWarehouse and Indexcomputer. Quite pricy, though. You might want to try calling IBM. Call: 1-800-388-7080 ThinkPad TransNote Inquiry for the part . And here are the prices that were posted on the discussion group a while ago.Sub-Battery (green):
FRU P/N: 02K6684 is old change to new FRU P/N: 93P5001 --- US$16.25Backup-Battery (yellow):
FRU P/N: 02K6682 --- US$57($49@ indexcomputer)

Ac adapter: P/N 02K6699 This is one of the parts that you can find either factory or replacement/OEM ones everywhere. Just for the reference, IBM sell it for $49 + shipping. Cheaper from buy.com last time I checked.
Other parts
SparePartsWarehouse and Indexcomputer are the two sites that I found which carry almost any part that are capable of braking off. Although it will depending mostly on how much you are willing to pay, most parts are really not worth it. You can always call IBM and see what their asking price is.
Indexcomputer special offer:
Good news! I chatted with Stuart from Indexcomputer earlier this week. They appear to have the most complete collection of transnote parts IN STOCK. Even better, he agreed to give anyone who refer to this website a 3 day select shipping upgrade for the price of ground shipping. Just make sure you put "www.transnote.us" in the "memo" of the payment page. Probably not as good as percent off or free shipping, but it's better than nothing. Email stuart@indexcomputer.com if you need any further info about any parts.
Pen
Digital Pen IBM no longer has it on their website. The above 2 spare part sites carry it for $70-$100. Here is a better choice. It is confirmed by many users that Seiko SmartPad pen works with TN, fits perfectly in the holder and has a better cap that does not break. The best source for this is a search on eBay. Shoot for a price <$30.
Pen Refill and AAAA battery They are still sold in Cross
Papar Pad Ok, I will not tell you where you can pay $50 to buy a stack of numbered paper. Just go to Staples and find a letter size regular pad. Please.
Memory
PC-100 SODIMM Since you can only add one stick, I strongly suggest to go directly for 256MB if you are planning on running Windows XP. IBM website has both 128MB and 256MB sticks. Other good sources are:My favorite. Also best memory suggested by many: Crucial.com - $106 for 256MB

MemoryX - $89.98 ; Kahlon - $77; Coast to Coast - $82 for 256MB

These are all RAM that is definitely compatible. There had been reports on memory with high density being incompatible, I'll see what I find and put the information in the "Tricks and tips" section.

ACCESSORIES
USB Floppy Although not all USB CD-ROM are bootable, all USB floppies are. If they are not, with the 1.44MB disk size, they are simply useless. So. buy it anywhere you find the price acceptable, You can find in any computer store. But if you insist on the IBM one, they sell it for $55 here. I suggest a 3rd party drive for less than $30.
CD-ROM It is almost impossible to recommend which CD/DVD drive you should use. It really depend on what you need it for. The only time I really hoped I have one was when I needed a clean installation. Everything else you can pretty much work by using network nowadays. Let me just give you some suggestions, then.UPDATE: It appears that most of the USB device "should" boot. The problem may lie in your USB port. If you are unable to boot, here are the steps to take. 1. Make sure the bios is set so that the high memory allow USB boot (Under config-> USB-> enable USB boot). After setting the BIOS, you need to turn the power off and on again, hit F12, and choose CD-ROM as boot drive. 2. Try a different USB port or port extender. A few things you want to think about when buying an external CD/DVD-ROM. First, speed. For faster drive (>6X), you will either need PCMCIA or USB 2.0. For bootable drive, you need either Portable drive bay/2000, IBM USB CD-ROM, or a few specific USB drives.

USB 2.0: Can be pricy since you need to add a PCMCIA USB card first. But it is a good idea if you find a drive that will boot with USB1.1 port and run at USB2.0 speed when needed. Right now, the only drive that I know of is the IBM USB 2.0 CD-RW. If I find any other drive that will work this way, I'll post here.

Bootable USB 1.1: I know only 3 drives that work this way. One is, of course the IBM USB CD-ROM for $179 (no longer available). The other two are HI-VAL External 4x4x6 USB CD-RW H446EU-15R  and Philips JackRabbit JR24CDRW as reported previously by other members.

IBM Portable Drive Bay & Portable Drive Bay 2000: While both these modules provide PCMCIA connection and changeable drive bays, there are two major differences. PDB2000 also have USB1.1 connection and the compatible drives are different- PDB support Ultraslim bay drives and PDB2000 support ultra bay drives. You will be able to use CD-ROM/RW, DVD, ZIP, LS-120, 2nd HD, etc. Bootable in both PCMCIA and USB mode and also use 3 AA battery to save your internal battery. Best choice if money is not an issue.

Remember, if you need to find anything, try eBay. Since these are not the hottest items, there is always a good chance you can find a pretty good deal.

Port Extender I beg you not to buy this. If it is a port replicator, I would have bought one myself. What it does is it first blocks your VGA, power, and USB ports and extend it to the black box a few inches away. The only difference I can think of with or without this extender is whether you need to plug in one or 4 connection cables.
Leather Portfolio for TransnoteHigh-Resolution Photo1

High-Resolution Photo2

  This is the coolest accessory you could get for your Transnote. A classy, stylish leather portfolio designed to transport IBM's TransNote digital notebook without hindering its usability. This leather portfolio secures your notebook, and allows you to unfold it, use it to transcribe notes and even utilize the pivoting fliptouch screen while still getting the benefit of the superior protection the leather portfolio provides. A Velcro Strap keeps your notebook securely in place and gives added security by preventing the laptop from falling out of the portfolio should the user neglect to close the zipper. This innovative leather portfolio even comes equipped with a removable thin black leather and neoprene Shoulder Strap for your added carrying convenience.

Buy it from the most reputable seller John. Contact him by email here. You can read all the positive feedbacks in www.transnote.com.

Exterior Dimensions: 14.1" L X 13" H X 1.75" W
Computer Compartment: 11.5" L X 12.6" H X 1.5" W
Rear Compartment: 12.75" L X 10.25" H
Weight: 1.66 lbs.
Others There are millions of PCMCIA and USB devices available that you can add on. If you need portable storage area, CF cards are cheap compare to other thumb drives. You can even use the 4GB microdrive if you want. Need to add a parallel printer? The USB to Parallel adapter will do the job. And, if you want better audio instead of the tiny single speaker in Transnote, adding a set of speaker is always a good idea.
SOFTWARE
CDs that comes with transnote include
Product Recovery CD-ROM for IBM ThinkPad TransNote Version 1.0

Disk 1

English/W2K-DT/Bootable

IBM P/N 23P2938

 

Product Recovery CD-ROM for IBM ThinkPad TransNote Version 1.0

Disk 2

English/W2K-DT/Non-Bootable

IBM P/N 23P3009

 

Software Selections CD for IBM ThinkPad TransNote Version 1.0

Applications & Device Drivers

IBM P/N 23P2939

The ISO of above files are available for download in the file section (Including the 4th disk which has lotus). I assume everyone who intend to use those files has windows 2000 key, these disks are only sold together with a factory unit of transnote system.