using an airport with an ATT router

I am having a situation with too many devices on a broadband modem. I just moved into a place and added a few onto my roomate's wifi.

I want to get a internet without taxing the network via wifi.

I have an apple airport extreme 801.11n, one of the first short square ones that came out a few years go. Can I run and ethernet cable out of an ATT broadband router into my airport and configure my devices on my airport so it uses my airport's signal and doesn't weigh down the current wifi?

I just want to know if it is feasible before I try and find out I can't trouble shoot..