Many people have had problems with certain Photoshop products and Leopard. For me, Photoshop Elements 3 stopped launching as of 10.5.1. It would reach the end of its launch sequence, and die with a bus error. Over on the Apple Discussions forum, I found a solution that worked for me:
Mac OS X Hints
http://hints.macworld.com/article.php?story=2007120814051788