well, to do this you'd have to be thinking about it when installing Windows, but...
If you created a 'guest' user (or some other name) that would let people login without a password, you could set up their access (let them surf or play games)
Make your user and install everything you want secure while logged in.
This could not be so useful, since I'm pretty sure there are key combo's to boot in Safe mode, where they could gain access to pretty much anything, but with Win98 at least, I think you're stuck 