I would go with the T60. If you value screen quality, you might have issues with the T43 since there may be imprints on the screen caused by the keyboard. I recall those marks as being quite noticeable on my T43p , especially when displaying black or dark colors. I don't know if all T43's had this p...

I would recommend Fedora 17 with the KDE desktop. Installation is about as straight forward as it gets, and it works very well with most hardware. It is a popular distro, so it is well documented. It also comes with GNOME, LXDE and Xfce, but your laptop should easily run KDE.

I would say thzt 768MB should suffice for XP while 1GB would be the minimum for Vista/7. My T21 runs xp and Lubuntu well enough with only 256MB.Of course, if you play games or run resource-hungry software, then 2gb should be the min.