WPA on the client side?

When implementing WPA on the client side, does it matter much whose WiFi
card you're using? Is WPA handled by the card itself, or software on the
computer.

I'm running WinXP SP2 on all systems. I have a Netgear FWG114P router. My
client side has a Buffalo PCI WiFi card. I had it all working with WPA, but
it seems when the key is renewed, I loose connection, and it won't recover
without a lot of messing around, only to loose it again.

I do have a 2.4GHz video link, in close proximity, and a neighbor across the
street, running WiFi, that I can see. Everything has been worked out,
channel wise, and coexist fine together, so long as I don't enable WPA.

Is WPA not an exact science yet?

Thanks,
Bill Crocker