Staring at a monitor all day, or even part of the day, can be very hard on the eyes.
If you're using a CRT display, one of the easiest things you can do to relieve eye-strain is to up your monitor's refresh rate. By default, your monitor is strobing at you 60 times a second. Pushing that up over 70 times a second will ease the strain on your eyes enormously, even if you can't "see" the flicker. To change this in Windows XP, just do the following: