Connecting extreme card to dlink router.

Hi guys. I have looked around for an answer first, and can't find one so....

I have an iBook g4, for which I have just bought and installed an Airport Extreme card. I have 2 dlink wireless routers, one connected to a cable service, and linked to my main mac via ethernet. It is broadcsting an unprotected wireless service, which my old dlink dongle connects to no problem at all.
I also have a router connected to an adsl service, which is protected, but which I can also connect to with the dongle. So I have a choice of 2 services available. Will my Airport card pick up either? NO! I can't get it to connect at all. It picks up my wireless printer, which is right next to the routers, so it's not a range thing, and my cousins ibook picked up and connected to my unprotected service without a hitch or change in settings.

Can anyone suggest a solution for me. I'm betting it's really simple, but I can't seem to figure it out at all!
Thanks in advance.

Well, I messed about with settings and such, and it's working now! I have no idea what I changed though!
One other thing though - the connection is very weak through the wall, but only about 5 feet away. Any idea if this is right? Cheers.

Fixed that prob now too! Pushed the aerial in harder.