Created a WPA password - All but 1 computer connects

I created a SSID and WPA 2 password on my D-link router stationed at my Vista computer. It connects along with my MacBook 2005 and my BlackBook 2006. However I cannot get my G5 late 2004 to connect to the SSID. It used to connect to the internet when my router was just default with no password set up. After I created the security the G5 doesn't want to connect. The other macs set up just fine.
Is the G5's wireless to old to connect via WPA 2? Is there another sort of security I should be setting up so my old azz G5 can connect through the routers security? Is there something to be setup in the system preferences? Theres really not much to it, so I'm confused as to what the heck is the matter? Someone please give some aid to my ignorance.

I put in the password and continue to choose the try again option.
In my system preferences, network pane I show that the airport information jumps between saying -
1. airport is turned on but is not connected to the internet. airport is not connected to the network.
2. airport has a self assigned IP address and may not be able to connect to the internet.

sweet! thanks for those who helped! that being, nobody.