Do you mean the contents of the windows themselves scroll up and down, or do you mean the whole picture rolls? If the contents of the windows scroll, you may have a malfunctioning scroll wheel on your mouse. Borrow a good mouse from someone, unplug the old one and plug the good one into the port and see if that fixes the problem. If it does, replace your mouse.
If the whole picture rolls, you may have a faulty monitor. If it's an older monitor, look for knobs or settings that adjust the picture and try turning them. If you have a newer monitor, or turning the knobs don't help, I'd suggest you try to find a computer geek to help you take a look at it.
Lovely Lillith, May 2004