Today I discovered that a font that I've been using for the past month is actually a MS Windows' True Type Font. I've just copied even more windows TTF into the Fonts folder and sure enough all of them work! I didn't even have to reboot or relogin for them to take effect.
Wheeee, off I go to show it off to those PC people. Thank you, OS X!
[Editor's note: This works as described, and probably as expected, since it's Apple's technology. What I can't remember from OS 9, though, is whether the fonts needed to be converted first.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20011108195111617