Somtimes the Refresh Rate of a monitor is set to low and causes severe eye strain, I use to have that problem. I would suggest setting your refresh rate to at least 72Hz-75Hz, some better monitors can handle 85Hz which is so much softer on the eyes.
Here is a link on how to change you Refresh rate in windows xp:
[url]http://support.microsoft.com/default.aspx?scid=kb;EN-US;q311403[/url]
If you don't have windows XP search on google.com for "How to change Refresh Rate on WIndows XX" xx being your OS like 98, Me, or 2000.
Hope THis Helps