Mark,
Though they'd physically fit (pins line up and all), I'd have serious
misgivings about the increased clock speed on the VESA bus burning up a card
designed for ISA speeds. In other words, I wouldn't try it, even if you don't
care about the ISA card, 'cuz when it dies, it _could_ take out the rest of the
computer with it. (Remember, unlike PCI, VESA is a direct connection to CPU,
RAM, etc.)
SCL