Let me list a few things that have crashed a clean Win98 gaming install:
Running Internet Explorer 4, 5, 6. Browsing safe websites.
(alternatively) Running netscape 4.x, 6.x. Again, safe websites.
Plugging in a USB device (this has got win2k and xp a few times for me also, not as bad as win98 of course).
Running a game.
Exiting a game.
Minimizing / alt-tabbing out of a game.