Oh, it can be done, but getting all the gtk dependencies is a pain in the ass. Some of the files in fontconfig have to be rewritten by hand to work on Darwin. Forget about fink, because that's like 5 releases behind current. And, oddly, fink doesn't even have all the current uptodate packages to support the version of gaim they do have, so that makes no sense.
Anyway, my iBook is almost as Linux-hot as my Fedora2 box at work.