Can't connect to Internet wirelessly but can with Ethernet

Ok so I have a Dell E6400 laptop running Windows XP. I have 2 other Dells running Windows 7--those connect to my wireless router no problem. The E6400 SHOWS that its connected (4 green bars in the icon) and that its authenticated but it shows no IP address and there is no connectivity either to my home network or to the Internet. I swapped out the wireless card (1397) with one of the other laptops and it worked fine so there is no problem with the wireless adapter card. Its must be something to do with authentication because its letting me "connect" in the sense that there are green bars in the status icon but no actual connectivity. I've updated to the latest driver--I tried using both Dell's wireless adapter utility and windows utility and can't connect. I've changed the workgroup to the same one the other computers are on. I don't have any filtering in my Linksys Router (E1000) its set up with WPA2/WPA mixed security with password and a/b/g mixed mode transmit. The wireless utility shows the security on the E6400 as WPA-Personal.

If I plug in an Ethernet cable to the E6400 it connects fine to the router--just not wirelessly.

Any ideas as to why its not getting an IP address from the router?