I'm using an original Airport card (in its very last incarnation, inside of a dual 1.25Ghz MDD) with WPA personal under Tiger and it works fine. Didn't do anything special. As long as the access point supports TKIP security you should be good to go. (AP in my case is the first square AirPort Extreme basestation, the ones without gigabit ethernet.)

The "forgetting the password" thing seems to be a perpetual problem with Apple. Editing your keychain and removing all references to an airport password *sometimes* fixes the problem. Sometimes.