One question though, do I have to have a special version of Windows XP for the tablet? Or only if I use the tablet features?
I wouldn't think that WinXP Tablet PC version is required for the X6x tablets. But it was included. It's just a superset of WinXP Pro. According to Wikipedia, the Tablet PC parts of the OS are available for free now for any WinXP (Pro?) license.http://en.wikipedia.org/wiki/Windows_XP_editions#Tablet_PC_Edition
I've turned off all the visible aspects of the Windows Tablet features (onscreen keyboard et al), but I haven't confirmed that the Thinkpad tablet hardware drivers (pen, digitizer, buttons) work in a non-Tablet PC version of Windows. I used to use Journal a lot for handwritten math notes, but no longer. I had thought of trying a non-Tablet PC version of WinXP sometime, but I don't know if that even makes sense now that it is sorta included in Service Pack 2.
I've found the X6x tablets to be truly no-compromise convertible laptops. I now rarely use the tablet features of my X60T, but the fact that it is still a physical tablet does not get in my way. It works very well as a non-tablet laptop. The hardware tablet features still occasionally come in handy (OS tablet features are not necessary in order to spin the display around to show something to a colleague, allow youngsters to play in MS Paint with the pen, be a full-featured e-book reader for PDFs, or cheat on games that don't expect you to have a pen, ...).
Consider looking for the WinXP downgrade discs if you get an X61T. After ordering my X61T with Vista from eBay, I called up Lenovo and ordered the "downgrade" XP discs. I haven't tried them yet, but they're on hand if I ever need to put my X61T into full-time service. For now (and until my X60T dies, which may be a while), my X61T is a secondary laptop which I've turned into a Win7 test machine. The way my X60T is hanging on, the X61T may serve as a Win8 test machine (alas, without multi-finger touch).
These tablets/convertibles hold up very well. I've not babied my X60T. It's been quite the commuter.