Which video card does yours have? Did you download the monitor inf file from cd or dell's website?

You can tell which card you have by looking in device manager for video adapter or by going into the display settings and looking at your adapter there. If you are using the onboard video, it is an Intel 845 chipset basic video. Check inside your computer for slots, I am guessing you may have an agp slot. I would consider getting a video card designed for the widescreen resolutions. Your monitor max is 1400 X 900 so it should be easy to find. The fact that the monitors limit is 900 is why you cannot go higher resolution. This should get you started

Here is a link to a description of cards and resolutions. http://www.cseced.org/AplusCert/Hardware/Video/video.htm You should be able to match up which card will work. As far as resolution, a card doing wxga or better is what you want for max display. I think your card may be comparable to in a Dell Dimension 2400, though not sure. This might help others to chime in. I have improved several lcd displays by changing fonts to improve readability, maybe thats the cheap way out.