From: Computerpilot on 07/08/2002
Reinstall your driver. Windows will default to a 640 by 480 resolution if your driver is malfunctioning or not installed. It will also stick you at 16bit or 256 colors.
You can check this in the device manager. Right-click My computer on your desktop; choose properties and then the device manager tab. You will seee either a yellow exclamation point for a malfunctioning device or a red 'x' for devices that do not have a driver installed. Even if the device is indicating that it is operating normally, you should reinstall the driver.
Also, make sure that you have the correct driver!
Hope this helps, post back if this does not solve your problem.