Maroon1's build with the Corsair 520 PSU from zipzoomfly would rock. As for OS why bother goign through all this if you aren't even going to run Vista for DX10 so I'd suggest Vista Home Premium 32bit. Half the awe-factor from these new games is coming from DX10 so it's a waste to build an entire PC for one game and not get it ^^ just my 2 cents