Widescreen monitor Help!

[systempat]

I bought a new monitor for my main system. Moved from a 17" LCD to a 22" Widescreen LCD.
Having a problem setting the resolution. Monitor is capable of 1680 by 1050 as it's maximum and native resolution. When I set the resolution to go to 1680 by 1050 (in Windows XP), that's not what I get. The desktop is BIGGER than the displayed window. Part of the image is off the screen. When I move the mouse pointer to the top, bottom, left & right, the screen scrolls a bit so I get to the edge. After some experiments it is displaying a resolution of 1440 x 900, but the desktop is 1680 x 1050. if I set it to 1440-900, then I get the desktop that fits.
Can't get it to switch successfully to 1680 x 1050. The lower setting is not what I want. This seems to be an issue of the Video adapter not the monitor. Hardware involved is a Gigabyte motherboard with the AMD-690 chipset. It's an integrated ATI video which is called an ATI express 1250. This has worked very well as a video driver so far. I tried updating drivers to the most recent Catalyst but it makes no difference.
Any idea of how to fix this ????? Other than the resolution the screen looks great.

Pat

[amdalex]

Did you adjust the screen size on the monitor?

[Alaron]

Try the "Auto" button on the monitor to let it recalibrate itself.

[systempat]

It's been thru the Auto Adjust a couple of times. Without solving this problem.

One additional note - It's using a VGA cable to connect. The monitor did not come with a DVI cable, which I did not know until I opened the box. I have DVI output available but need the cable. So it's connected with VGA for now. DOes that create a limit on the signal ???