It's an 8x/4x. Gosh, that looks nice
Sounds like the video card is trying to get the monitor to display what it can't display. Most likely it's a "refresh" rate.
I would check to see if windows xp recognizes the monitor properly not some "standard" or "plug and play" crap. If it doesn't find out who makes your monitor, find a driver for it and install.
Once you do, you have the option of hiding all the settings your monitor can't support. If this is indeed the problem, it will avoid further outbreaks of the error.
Once that's done a re-install of your AGP drivers (or better yet, download new drivers) should get you going.
Hope this helps....