If you can't get a PowerPC application to launch on an Intel Mac, try this odd-sounding workaround: hold down the Command, Shift, and Escape keys together as it's launching. In my case, I was not able to launch PowerPoint v.X successfully. I tried the solution documented in this article on Apple's site, but it didn't work for me. The odd keystroke combo, however, got PowerPoint up and running.
[robg adds: I have no way of confirming this, as I've never had an issue launching Office v.X (and I do have Motion 2.1 and Final Cut Pro 5.1 installed, two apps listed in the Apple article). If anyone can confirm or refute this hint, please comment!]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20080428184654995