So if I was looking for an older Thinkpad to throw something XFCE flavored onto, what are some model numbers to look for? I'm basically just looking to do word processing/browsing, but I assume I'll have to jack up the ram, maybe replace the main drive with an SSD...
Depends on what screen size/resolution you favour, and the type of keyboard.
I like the older keyboards and I'm ok with 1366x768 so I'm happy with an X220 with 8Gb RAM and a 256Gb ssd (sata). I know many people would find that unacceptable.