Hi,
If you have integrated graphic card (for instance: GeForce 4) and aditional graphic card which should actualy be you primary or default, make sure to clean up the drivers of all graphic cards and other stuff that is already included with WinXP with Driver Cleaner 3. Make sure, that you DO NOT clean up the drivers for your sound card. Even if you do not have 2 graphic cards, do the driver cleaning, and then install the latest driver for ur Nvidia. All other stuff, except sound drivers, should be cleaned up.
Once when u install Driver Cleaner 3, u'll c that there is a list of things that can be cleaned up. Clean up all of them - except sound drivers.
This helped me - I had no problems after that - but also it may produce some negative effects on ur computer.
Good Luck.