Gaming Graphics Freezes

Ok to start off I'm not sure if this forum is the right place for it but I couldn't see any "technical assistance" forum.

Basically whenever I play any game the game graphics will freeze. It can freeze for up to 15-30secs and then will automatically unfreeze itself. I can still hear the audio as normal but the graphics freeze. As soon as it freezes, I can CTRL-ALT-DEL instantly. However if I go to task manager and go back to the game it is still frozen. This happens at random times, sometimes my pc will have only been on an hour, other times it would have been on for 8.

I will try to be as thorough as I can with my PC specs so maybe you guys can help me out.

Core 2 Duo E6300 @ 3.0ghz
4x1gb PC6400
EVGA GeForce 8800 GT 512MB GDDR3
2x250GB 7200 RPM hdd's
520w PSU - getting 4.95-4.97 on the 5V rail, 3.30-3.31 on the 3.3V rail, 11.97-12.10 on the 12V rail
Windows Vista Ultimate 64bit

Temps:
CPU idles at 40-45º and rises to 50-53º in gaming
gfx card idles at 45-50º and rises to 58º max in gaming
hdd's are around 25º

The games were running fine up until about a month ago. At the time I had a 7950 and only 2gb ram on windows xp. I then upgraded my gfx card and bought another 2gb ram. I decided to go for windows vista 64 bit to take full advantage of my ram. My PSU was more than ample (it is an expensive one) for that setup. Is it enough for the new setup?

Help is appreciated

Regards,
Straknos

Stab in the dark, are there any hefty background apps running, something that could suddenly kick in intensively for 30 seconds, but only do it once/twice a day?

When my antivirus (NOD32) updates it's virus signatures daily it causes a massive system overhead for a short amount of time.

OCZ ModStream 520w ATX2.2 Power Supply. Intel TAT but that doesn't work in vista so i switched to CPUID Hardware Monitor. Video Drivers are completely up to date. Has there been any issues with the newer sets then? My old 7950 was on the 163.xx drivers iirc.

No nothing like that. Also, it is only my graphics that freeze in game, nothing else freezes.

as I said in my initial post my gfx temps are 45-50 idle and up to 58 in games

Thanks in advance
Regards,
Straknos

Bench mark your video card with a utility thats built into a game like counter strike, or use the nvidia benchmarking tool