If you had a plug 'n' play monitor, Windows would already know what resolutions are supported - otherwise, you should always change the resolution from the display properties, where it will ask you if you want to keep the new settings. This way, if it doesn't work, wait 15 seconds and it will restore the original settings. You should only have the display settings in the tray if your monitor supports all of the resolutions your card does (because it's far too easy to click the wrong setting, and it doesn't confirm).
To fix it, what you need to do is boot into Safe Mode. The easiest way to get into safe mode is to hold the CTRL key, starting right *after* you see "Starting Windows 98"... you'll then get the boot menu, from which you can choose Safe Mode. Failing that, shut down the power (or CTRL+ALT+DEL) in the middle of the boot and it will come up in Safe Mode automatically
Once in, hit the display properties, settings, and hit 'Apply', and answer yes to the warning message, then reboot. You will then be in 640 x 480, 16 color mode, from which you can then change to a supported setting.
Hope this helps.
[This message has been edited by Justin (edited 04-01-00@7:48 pm)]