I'm not sure if this is new to Panther, but I can't remember that files and folders could be named with a slash (/) before.
[robg adds: I'm not positive, but I'm pretty sure this is new in Panther -- if it's not, please comment as such and I'll remove the hint...]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20031114045400715