[dba-Tech] New router network puzzle

Hi All,

I have a broadband internet network consisting of the antenna, POE, 
router0, cabled router1, cabled router2, two computers wireless 
connected to router1, and 3 computers wireless connected to router2.

Router0 is at the POE, router1 and router2 actually serve as wireless 
access points.  All was fine until router0 crapped out today.  (I'd been 
having performance issues for weeks, but thought it was with the ISP.)  
All three routers were D-Link DL 514.  I bought a new NetGear WNDR3400 
to replace router0.  Now, comes the issue.  It wants to establish its 
own network - which for the nonce I have allowed, because that got me 
back online.  I want it to join the existing network - using the SSID I 
already have established.  How do I do that?  I tried just changing its 
SSID name and feeding it my WEP key.  It said that SSID already existed 
and refused.  How do I coax the new router to join the old network and 
take over for the old router that crapped out?

Thanks,
T