Connect non wifi computer to airport base stationwith ethernet?

I am reasonably sure this is a stupid question for someone who understands this stuff, but networking isn't my forte.

I have been connected to the internet by broadband cable for quite some time.

...but I wanted to share that connection with my other computer, neither of which have an airport card, an older G5 and a intel mac pro.

So, I got an airport extreme base station, thinking that I could plug in the broadband and access it from both computers using the ethernet plugs.

Well, it doesn't work...at least I don't know how to do it.

I know the airport station is fine because I accessed it via my notebook which DOES have an airport card.

HOW can I hardwire the desktops into the airport station and share internet and files without buying airport cards for them?

Is there anyone who can walk me through this step by step?

So to start with did you just have a modem that connected to your notebook by ethernet cable?

If so you need to connect the modem to the WAN port of the Airport Extreme and connect your notebook by ethernet cable to one of the other ports on the AE.

Now start up Airport Utility on the notebook and run throught the setup wizard for the airport extreme.

You can now disconnect the cable to your notebook and connect the other two machines.

You should now have internet access by cable and by wifi.

Thanks for your reply.

The problem ended up being the ethernet cable, which worked fine with my broadband receiver, but airport didn't like it at all...I wasn't aware that it was a crossover cable instead of a plain ethernet cable...once I switched that out, it works fine....but now I'm left with one more question:

I want to access files from other computers on my new network, but I don't know how to access them.

In system preferences/sharing...it tells me:

Computers on your local network can access your computer at: hombres-mac-pro.local

..so where do I type that in to transfer files from one computer to another?