Optomize for Mac and PC

Hello

Im in the process of creating a full flash website. Im running into a bit of trouble with optomizing the page for mac and pc. My animations run smooth on my home computer (pc) but while at school it loads slow and animates poorly on their macs (g4). Im also running into some trouble with my preloader actually preloading in safari, it just waits till its loaded and then skips it all together.

I know that there is a way to optomize flash files for macs… something like

www.sixstation.com

while loading the pc version of the site on a mac its slow, but the mac version runs fine.
any ideas on some stuff i could do to get my movie running better, and platform specific optomization that would reason for him creating two versions?

thanks