Strange 8800 GTS 320 issue.

Hey all. I've been having a problem as of late, which I haven't really considered a problem up until now.

My problem is this, sometimes when I am playing a video, and using a program such as Photoshop or 3ds max, my video will at some random point become 'graphically corrupted'. What I mean by this is that the video becomes a mass of pixelated, well, pixels. The audio still runs fine, and my media player (Windows Media Player 11) still works perfectly fine. I can shut the player down, and load it up again, and the problem remains. Sometimes the video corrects itself after about five minutes, however, most of the time it requires me to load up a full screen program (like a game) to fix the issue.

Anyone have any ideas what this could be? My 8800 isn't overheating, and is running at 60* average, never climbs above 65. I thought it might be my codec pack, so I changed from K-lite to XP codec pack, but that hasn't fixed the issue (however, from what I can see, both packs use almost exactly the same codecs).

Could it be nVidias drivers? Or is there something screwy with my card? (It runs benchmarks and games like a dream)

If anyone could shed some light on my problem, it would be grande!

Cheers in advance.

(Using Windows XP SP2, with all the latest updates and drivers. It also happens with all media players, including VLC and Quicktime)

EDIT: I tried to take a screenshot of the 'pixelerisation', however, when it came to pasting my screen-grab into Photoshop it had some kind of a ghost effect. As in, the media player screen, which should have been all pixelated and green, was just showing as solid black. Wierd.