If it is a CRT monitor the problem might be alleviated with a better monitor. CRTs flicker at refresh rates lower than around 45 and have been known to cause some motion sickness when viewing (along with eyestrain and headaches). And I too can vouch for that as I have pretty intense motion sickness, and I got sick all the time playing games before I upgraded my system. See if you could possibly find a friend with a better monitor who would be willing to let you try one in an attempt to isolate your problem, before you consider spending money on it.
