Assuming you have Windows XP, do the following:

1. Close all your windows.

2. Right click on an area of your desktop that does not have any icons.

3. Select "properties"

4. Select the "settings" tab

5. Read the number (mine says 1280 x 800) in the screen resolution area

Report back with that number. I'm guessing it's 800 x 600. If that's the case, the way it's currently set up will probably not work too well.