Re: Building new but old gaming computer.
Well I was going to say xp however I noticed that you have 4gb ram and the 64bit windows xp is supposedly crap and doesn't support much. You will only be able to play directx 9 games anyway but I would say go with windows 7 on that setup unless 32bit xp can see all 4 gb but I'm not sure it will. Hope this helps.
I'm not sure about the motherboard though
AMD Phenom II x6 1045T @ 2.7 Ghz, 8Gb Corsair Vengeance Ram, crucial M500 240GB SSD, 500GB WD
1.5 TB Seagate, XFX Radeon 6670 1Gb GDDR5, Windows 7 Professional 64bit