My roommate came up with a clever way to force iTunes to stop playing after the current song when using the Party Shuffle.
Simply create a playlist with no songs in it, and switch the Source pop-up on the bottom to that list, and it will refresh with a blank list. After the current song is done playing, it will stop.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20050121154724925