I too have IBM T40's. actually two. one running Debian lenny, and another, at the moment, running fedora 9. I love them, but they are just starting to fall apart, like the key board and some screws are missing. They are like old company throw away computers so. they are very nice machines and have been very good to me. I heard very good things about the levono T61, but it is like just under 2000 USD where i have looked. I did the "search for like threads" option thing when i created the post. I would doubt that I would have many issues, but I only know the T series so. I'll probably end up giving into the T61 temptation anyways.
but still, if anyone knows how good it is with linux, please, do tell.
PS. what wireless card and what debian did you try.