Here is how I got mine working... first try for me also and I finally 
got it going.

System->Administration->Network
    Edit wireless (mine is eth1) so it is not active on boot

System->Administration->Services
    Disable network and wpa_supplicant
    Enable NetworkManager, make sure ipw3945d is also enabled

edit /etc/wpa_supplicant/wpa_supplicant.conf so it looks like

        ctrl_interface=/var/run/wpa_supplicant
        ctrl_interface_group=wheel

        network={
            ssid="cd"
            proto=WPA
            key_mgmt=WPA-PSK
            pairwise=TKIP
            group=TKIP
            psk="yourpre-sharedkey"
        }

Reboot (using Gnome) with NetworkManager running it shows me available 
wireless
networks, I can select mine, it asks for the psk (which leads me to 
believe it is not
reading the wpa_supplicant.conf file but I have it in there anyways) it 
will save the key for you.

That is how I got it working.