Slow on a Mac, here's why

I have an old G4 Dual 450 Mac that I’m testing my animation on. My animation was running really slow on this Mac, but fine on the PC. I narrowed the problem down to having wmode set to transparent.

wmode="transparent"

This runs fine on the Mac:
http://www.iuinfo.indiana.edu/projects/olympiad/

But this page has wmode set to transparent, and runs really slow on my Mac:
http://www.iuinfo.indiana.edu/projects/olympiad/index_trans.shtml

(Both play fine on my PC)

Anyone else seen this problem? Any ideas? I would really like to keep the wmode set to transparent.