You've probably already bought everything, but as an FYI for future purchasers, I have Vista 64-bit (SP1 of course) with an ATi Radeon 4870 (beauty of a card! Runs everything maxed out!) and 4 GB of RAM. I'm pleased to report that Sins works flawlessly. I've never had any crashes or problems whatsoever in the months that I've been playing. I highly recommend the setup!
A friend of mine owns the 4850 and sometimes his graphics card can't keep up at 1024x768 when zoomed in on the action (<20 FPS with settings on "high" if I recall correctly), whereas my 4870 will run smooth as butter at 1920x1200 (Everything set to "highest"). The GDDR5 VRAM makes a world of difference.
