usually unstable programs. Time to get rid of windows 98. It's to unstable to deal with. The only big hardware issue it would most likely be is a lack of ram, but it usually just gets painfully slow.
Before getting rid of your os, and probably having to upgrade your hardware if you were to move to windows xp, there are a few things you can do so that it doesnt crash.
You can to the typical, hard drive scan, virus scan, spyware scan, make sure you have updated windows, and updated drivers. If the freezing resulted from updating drivers, than go back one version.
Did this freezing happen from a major change in the system? Or did it happen suddenly?