Hello,
the problem is that Windows 98SE has not been supported by even Microsoft for over a year now. So that every vunerability that affects all version of Windows has not been patched. Which leaves your OS open for all sorts of problems.
The main suggestion that has been given is about upgrading. But from the sounds of it Windows XP will not run on that machine. Might be time to shop for a new one.
Cheers,
Mak