Connecting a Wireless router to a modem/Wireless router, Help!

(I posted this first in "Wireless Networking" and have had no responses for a few hours so I decided to post it here also.)


So I'm trying to get a certain device (Nintendo DSI to be exact) to work with my modem/wireless router, but the DSI can't use WPA. I have other devices connected to the modem/router through WPA. But, I don't want to change my modem/router to WEP, and have to change all my other device's settings.

So what I think to do next is use an extra modem that I have that the DSI can connect to. I connect the extra router to the modem/router via Ethernet, and when I try to get internet from the extra router, I can't. Is there something I can do to get this situation working?


Details

ISP: AT&T U-Verse

Modem/Wireless Router: 2Wire 3800 HGV-B

Extra Router: Linsys BEFW 11S4


Promt advice will be much appreciated