I suppose you have Windows Vista 32-bit, so I will base my instructions on that.
1. Download the latest nVidia Display Drivers for Vista 32-bit (
http://www.nvidia.co.uk/object/winvista_x86_175.19_whql_uk.html), but do not install them yet
2. Uninstall your current
nVidia Display Drivers through
Windows Control Panel - Add/Remove Programs3. Restart your computer (after the restart the resolution might be messed up, but that is just temporary)
4. Install the latest nVidia drivers, which you downloaded earlier
5. Restart your computer again
Now you should have the latest drivers installed for your graphic card. If you have Vista 64-bit, let me know and I'll give you another link for the driver download. Hope this helps.
:ps: Is your computer a laptop or does it have an integrated graphic card? If so, you might be able to change the graphic card's memory size in the BIOS setup.