Andrew Dalke writes about his painful attempts to install Ubuntu Feisty on a Thinkpad T23. I've had a T23 and ran various versions of Ubuntu on it happily. When it works, Ubuntu (and Linux in general) is great; when it doesn't work, it is painful (but at least I can fix it, unlike, say, Windows).
One thing, though: the T23 doesn't support USB2. Using an external hard disk over USB1 is very slow and uncomfortable. Also, I wonder what sort of an install disk Andrew used. It sounds like a server or alternate install CD -- the regular desktop CD installs X and everything else for you.