connect Airport Extreme to another modem/router?

I've go an adsl internet connection and a crappy adsl router/modem/wifi thing that I was using with it until this morning when I decided to treat myself to an Extreme.

What I want to do is connect the Extreme to Lan port 1 of the other router and basically just have it take over all the wifi, dhcp, firewall blah blah blah and just use the other as a modem. Is this possible? I've been googling around and I think I need to set the other router into bridge mode? is this correct? I've been messing around all afternoon playing with settings and it's annoying other people who are sharing the internet connection so I don't really want to start messing again until I understand exactly what to do.

Consultant said:

Easiest way is on old router
- Turn off wifi (unscrew antenna if possible)
- Turn all security off (well keep admin password as something non deafult of course)

Then connect Airport station via ethernet to your model, and set it up.

If you post name and model of your router modem combo, maybe someone can help with more specific instructions.

Click to expand...

Yeah I can easily turn wifi off but how would this stop it using dhcp? I've tried connecting the AEBS to the other router (which is a ZyXel 660) and set the AEBS to use dhcp to share a single IP address but then the Airport utility complains that the AEBS has on internal IP to share?