If ilexius's suggestion does not work (wpa support is iffy in the Network Manager that comes in Hardy) then you could try loading the newest version from the Network Manager maintainer Alexander Sack. It has better support for wpa2. I have been using it and it is very stable and works great. To get the latest version you simply add the commands below and it will automatically upgrade.
Open system>administration>software Sources and click "add". Add these lines (one at a time).
Code:
deb http://ppa.launchpad.net/network-manager/ubuntu hardy main
deb-src http://ppa.launchpad.net/network-manager/ubuntu hardy main
Reload and close. The upgrade manager should appear with the upgrades listed and just hit OK. You may have to reboot I don't remember.
Enjoy