This sounds to me like we are talking about some wide screen resolutions, correct me if I am wrong. You may have to tinker with your graphics settings because it could be "stretching" SW to fill up your screen. Right clicking your desktop brings up the quickest access to some of these settings, but it really depends upon the card. There are some Maintain Aspect Ratio settings that could be applicable.
I would also try Microsoft Update, as much as I hate to admit it; they usually do very well with the Dell monitor drivers. I would also make sure your graphics driver are the most up to date SW supported. If that doesn't work try some of the more recent unsupported revisions, but of course that is at your own risk.