Just sharing my experience. I was able to get Sins to work on my Macbook using Parallels 5 and Windows 7. I had to use Win 7 instead of XP because I can't upgrade to Service Pack 2. To use Impulse, you have to use IE 7 or higher. You have to have Service Pack 2 to get IE8 on XP.

I tried using Fusion 3, but it crashes every time I start Sins.

You should disable the magic corners in Parallels because you tend to move your mouse to the corners of the screen and Parallels thinks you want to go back to the OS X desktop.

I hope this helps any Mac users who were on the fence about purchasing this incredible game.