Screen frequently changed resolution

I'm having a problem with my PNY GeForceFX 5200 PCI, with the latest
61.21 WHQL drivers on WinXP Home. I've had the problem since I first
got the card. I then had the 56.72 drivers.
Whenever I do anything related to context menus created by my nvidia
drivers, the screen will change resolution to one it can't display
then immediatley flick back to what I had before. This will happen
when:

- I right-click on, or load (including at startup), the taskbar icon.
- I right-click on a file with associated nvidia entries: for instace
AVI's with the 'play on my TV' command. I haven't a TV.
- I load the advanced display tab in Display Properties.
- I load or switch to the nvidia properties panel, from Control Panel
or Advanced Display Properties.

Why does it change resolution like this, and what can I do to stop it?