WMP slow video since SP2

Hi,

Since I installed an Nvidia card recently, I had to install SP2 on XP to make the drivers work.

However, since doing so I haven't been able to use Media Player to play videos. The result is a poor frame rate (a frame every 5 seconds or so if you're lucky) and the rest of the machine becomes highly unresponsive too until I stop the video playing. I checked the CPU/RAM usage during playback, but the CPU usage is extremely low, as is the RAM usage.

I've updated Media Player from 9 to 11 but the same issue remains.

I've seen a few posts about people with similiar issues, but I haven't been able to find any resolution.

Don't suppose anybody here might have any ideas?

Thanks.

Edit: It's come to my attention that no video program plays videos properly anymore. They constantly skip frames and any other PC activity, such as dragging another window, MSN alerts and so on will cause them to freeze up.

Edit 2: Might be related to the Nvidia card as performance improves with hardware acceleration turned off. It's not really watchable with it off thanks to the poorer playback performance, but the PC doesn't freeze up or skip frames constantly in other programs.