I may have to come up with some concrete examples when I return home, but I recall having some difficulty with implementing WPA for my home network consisting of both PC and Mac.
One of difficulty was in different ways PC and Mac handle the passphrases; Mac may need $ in front of the passphrase where PC doesn't. Another thing was that there seemed to be different bits used; I can choose from say, 64 or 128 bit on PC, but only 96 bit on Mac.
(this is off the top of my head; I could be wrong about exact number of bits; but I know for sure I didn't have same choice on either computer)
Mainly becaue of different bits, I got too confused and settled on WEP. Wonder if anyone could enlighten me on that?