Bellsouth DSL wireless help with Westell 327W modem

I am trying to figure out how to configure the wireless setup and keep running into the same problem. The computer in question is a brand new macbook with airport wireless connectivity. The modem is a Westell 327W that was supplied to my parents some time ago when they first signed up for DSL through Bellsouth/AT&T. Previously the wireless internet worked fine with a Dell. The Dell is unfortunately dead now, so my mom (who is old and not that great with computer techie stuff) went with the new Mac.

Here is the issue:

When the ethernet cable is plugged into the Macbook the internet works great but when the ethernet cable is unplugged and I try to conect to the already established home network, the new computer will not connect to the internet. The Mac “sees” the network but will not connect. I know that the Mac wireless hardware is OK because I took the Mac to my sister’s house and it connected to the wireless network just fine over there.

I had an extremely long and detailed conversation with the tech support person but the end result was a bust, he really didn’t have anything to offer. He tried to refer me to a pay-per-call support line but I declined because by that time I wanted to scratch my eyes out and I had already been on the phone long enough. Plus I don’t really like the idea of paying for tech support when my parenst have been paying for DSL all these years.

I have tried resetting cutting everything on and off including hard restes but to no avail. I had the tech reset the password but that didn’t work either. I am sure all the usernames and passwords are correct. I tried to connect to a Belkin wireless modem of my own and that didn’t work either.

I am convinced that there is some simple setting somewhere that will allow everything to work once I tweak it. I know the modem works and I know the computer works, I just have to get the two to talk to each other.

Any ideas?