DPI (dots per inch) settings control the images resolution on your computer, the higher the DPIs the sharper the image will be. You can change the DPI settings to fit your liking. On windows XP right-click on an empty area on your desktop and go to properties>settings>advanced
You can change the DPI settings to:
Normal size (96 DPI)
Large size (120 DPI)
Normally the computer is set to 96 DPI, most applications are written to fit this setting, if you are having problems with applications not displaying correctly because it does not fit your screen, most likely the problem lies on the DPI settings.
You most likely will need to reboot the computer for the settings to take effect.