I had this exact problem for two weeks with my kt-7raid.  Happened in either win2k or win98se.  I'd get a crash every now and then, usually in a Vxd.  Problem turned out to be ram that the system didn't quite like, though it worked fine in a 440bx board.  Replaced it with some new pc133 ram, and it hasn't crashed or rebooted itself in close to a week now.