Go into Safe Mode and use the System File Configuration utility to set the machine to Base Video (VGA). To get into Safe Mode, repeatedly tap the F8 key as the computer is starting up. Then do Start>Run>msconfig [OK]. The System Configuration Utility appears. Click the BOOT.INI tab. Under Boot Options, check "/BASEVIDEO." and click OK. Reboot the computer into Regular Mode. Now set the resolution to the correct one for your monitor. Don't forget to go back to the System File Configuration utility and uncheck "/BASEVIDEO". Apply and OK out. You don't need to restart immediately, but the next time you do you'll get a dialog saying you've used the Utility. Just tick the box that says in effect, "don't bother me about this again".
MS-MVP - Elephant Boy Computers - Don't Panic!