Having the same problem. i have a dell 8200 with xp. it's about 3 years old. monitor is a M992 crt monitor with Nvidia Ge Force4 MX 420 and i've updated it with the latest drivers and everything. I've checked the display setting and played around a bit with the refresh rate and resolution to try and get the screen to widen. I always keep my res @ 1024 x 728. i have the refresh rate @ 85 right now. I widen via the osd controls on the monitor and i still have two black spaces on either side of the screen. The monitor is fine and i have no problem reading anything but i just can't widen my display so that a page will fit the entire screen.
I'm up for some advice.