When I purchased my Thinkpad T60 (nearly 18 months ago now -- how time flies!), the Lenovo sales staff was unable to help me find a notebook with Linux preinstalled. Maybe this has changed recently, but you're better off just buying the base Windows version and putting your favorite Linux distro on top of it.

http://www.thinkwiki.org is the best resource I'm aware of for Linux + Thinkpad installation tips.