It seems that no matter what the performance settings on your Monitor and Video card allows.
By default without making use of the tweaking software that comes with most driver cd's, XP
will not allow your refresh rates to exceed 60 which can and does cause headaches, eye strain,
blurred vision, etc after a period of time looking at the monitor. From what the artical states
you should set your refresh for monitor and videocard to at least 75 - 80 to save your eyes.
Higher if they will allow it, you have to use a utility to do this, and you also have to make
sure it loads on boot up as Windows XP will return the registry settings to the default of 60
on the next boot...

thought if anyone was noticing issues like this, it might make a difference for you..