Guitar Hero World Tour freezes

I am having trouble with Guitar Hero World Tour crashing on my machine. It's an iMac 2.16 GHz Core 2 Duo running 10.6.2. When I start playing a song, the game plays fine, and graphics are smooth. After a few minutes pass in the song, the graphics will freeze, and the music will keep playing for another few seconds. At this point, I have to physically power down the computer and then start it up again. This happens about 50% of the time, so occasionally I do get through a whole song.

I brought this issue up to Aspyr and they were not helpful. Has anyone else experienced this or can anyone give me some ideas on what might be causing the issue?

Thanks.