Most pc games work mainly on windows so there is not option left. Anyway your machine sounds good for gaming.
Tbh I don't think it really makes a huge difference if your using XP, Vista or Windows 7. Maybe a couple of frames here or there, but it shouldn't be more then that. But my recommendation is Windows 7. I've had some games (namely Dark Messiah) which crashed constantly under XP with DirectX errors but ran perfectly under Vista (I'm presuming this is due to Vista's more stable graphics driver model). By now most of the issues NVidia had with Vista's driver model have been resolved (for a time NVidia drivers caused more crashes on Vista machines then anything else). However Vista (and so Windows 7) have _far_ better scheduling algorithms and so make better use of a multi-core PC. Windows 7 especially is optimized to take better advantage of the latest hardware. Today you could get away with using XP, but I suspect in a few years with mainstream CPUs comming out with 8 or more cores, you'll start to receive noticeably worse CPU usage if you used XP over Windows 7. But for the best performance I've heard of for games is to run a copy of Windows Server 2003 (essentially server edition of XP) or 2008 (essentially server edition of Vista) all stripped down of their standard features. The server editions often loose backwards compatability with older hardware in order to gain extra performance. Lots of people often use Windows Server as a workstation OS too for this very reason.
i dont know which is better. . Bt i use the window xp and it is free from prob. .and it is very smooth for me
You can say Windows 7 (which is definitely superior over Vista) although Windows XP is less demanding on your computer and therefore will run games more smoothly.
It depends on what type of game you want. Windows 7 can run pretty much anything that was able to run on windows xp, but some tweaks may be necessary.
nothing is better than windows. And if you combine it with good graphics card,processor and ram more importantly a big LCD wil give the ultimate gaming experience.