If you're talking about a laptop PCMCIA card, it probably has an
antenna on board.

If you're talking about a PCI card that plugs into a desktop and has a
removable antenna, I'm sure the power amplifier has protection
circuitry.

A high SWR doesn't necessary damage a transmitter that reduces the
output power as the impedance goes awry.

I don't think that the designers of 802.11b/g gear are going to be
counting on a good SWR at the output anyway, as people are going to
shove the computer in the corner with a bunch of cables on it in random
orientations/locations with respect to the antenna.

73, Dan