Help!!

i'm trying to connect a linksys WRT54G to my vonage router, a linksys RT31P2. My connection works fine when I have the vonage router plugged in. When I try connecting the other router to my vonage router, the WRT54G gets no connection. I then tried vice versa I hooked my computer up directly to the WRT54G and according to my LAN connection, I was connected to the internet but when I tried using internet explorer, it could not access any webpages. Even when using the setup wizard for the WRT54G it reported that the router could not connect to the internet both times when I had it hooked up as the slave and the primary router. Any ideas why this could be happening? I honestly have no idea what to do and need wireless for other computers in the house