Windows 98 isn't that old, some games at Best Buy in the $10 area are Windows 98 compatible.
As for driving games, I don't really play those so now sure what a good one would be.
Puzzle games. I like Jewel Quest, Mario games which are all available to download from CNET.com, just don't install the toolbars for some of those games. They play really well in Virtual PC, so on an actual Windows 98 machine they should work really well.
There is another option and that is console emulation. Turn Windows 98 into an Atari or NES, etc. A good place to go for that is
http://www.emulator-zone.com/.