My F@H is running under VMware in Windows XP
on a one engine of a 4 engine Mac Pro running OS X
When you finish this work unit consider trying out the Mac SMP client. Double points on a really fast system like yours.
With the intro of SMP v6 betas, look into it. I think that josephw is running such a creature, and he is consistently in the Top 5 of FReeper folders.
Here are a couple of notes on the SMP client under OSX: