Check your device manager in XP and make sure the drivers for the video card are installed. Or go to the web page of who made the laptop and see if they have an updated driver for XP to allow the display to work properly. The only other thing I can think of it try to adjust your refresh rate. Sometimes if it's set to high it yanks away some of your screen.

Another thing is some laptops have a Function key which you press down and hold and it will let you adjust the brightness and contrast on your screen. See if there are any ways to change the size of the screen.