Simon is probably right about your system being corrupt.

However, I would try running AV, SpyBot and AdAware in safe mode and running the Trend Micro "Housecall" just to be sure it is not a malware conflict causing it.

Also, kill the screensaver and power saving features in the display Manager and BIOS.

98se is a bit flaky, and you do not have a lot of RAM.

Good luck