I know that you can use a series of AirPort base stations to extend the
range of one -- by acting as relays, I assume. Is there some way of
doing the same with a laptop with a wireless card? I have a PowerBook
G3 (Wallstreet) with OS X and a wireless CardBus card, and since it is
more centrally-located in my house than the AirPort base station, I'm
wondering if there's any way to make the PowerBook act as a relay.
(That PowerBook's screen hinge is broken, so it is stuck in one place,
acting as a desktop and always on.)

Also, if I did have a relay like this, would it adversely affect the
connection speed? Or will it still work at the same speed?