Going back to vist or xp

I just installed W 7 from vista 32 bit.But the games i play like CSS and COD2 suffer in resoultion and FPS.What would be the easiest way to go back vista i know i would have to nuke my hard drive im ok with that.I downloaded XP and wont let me intall due to me runing a newer OS.Any advise would go along way i know theres a lot of questions THANKS

PC- 2.2GHz intel celeron , 2 GBs RAM , Nvidia 8400gs

You'll have to do a "clean install" of Vista. You'll have to wipe the hard drive clean and start from scratch now.

You can download a copy of "Gparted" which is a free boot-disk partition program based on the Linux kernel. It will boot up and then you can wipe your hard drive and partitions clean. Then re-install Vista.

You can use EasyBCD to Manage Bootloader for "Uninstall the Vista Bootloader (use to restore XP)". I have not tried it myself but there is a purpose in this option.

It might be easier to troubleshoot the performance issues than go back to XP. I don't see why COD2 and CSS shouldn't run just as well under Windows 7. If you make a new thread on it we can help find out

An 8400GS isn't going to deliver sufficient FPS unless most settings are at their lowest and the resolution is 1024x768 or lower... NVIDIA's current IGP has more power than the 8400GS in some cases. There are some really affordable gaming level GPU's below the $50 mark such as the ATI 4650, that would fix any FPS/resolution issues.

Maybe you should see what the problem is before going back to vista