If the PC isn't going to be re-set, can I suggest that you: 1) Get a good AV prog installed and keep it up-to-date. 2) Get a firewall - ditto, and 3) Install all appropriate Windows critical updates?
For reassurance you can run progs like Spybot Search & Destroy and Adaware, but if it ain't broke...
There ain't nothing wrong with a W98 PC, but it still needs protection to the right level.