Network G5, MacBook & PC laptops with Airport?

I have an I Mac G5 currently running on Comcast cable Internet service (ethernet) in a house with a MacBook Pro and 2 Dell PC laptops.
I have a never-used Airport Extreme that's a couple years old and wondered if it would be possible to network them all through the Airport...?

yes, airport extreme and airport express are both WIN/MAC compatible. You shouldnt have any problems. Even works with XBOX/PS3 wireless cards.

Call the cable guy?

Thanks for telling me that; I am new at this. Should I be able to hook up the Airport to Comcast on my own, or will I need to have them come out? Nothing like blowing a day waiting for the cable guy! Will I need any additional hardware? Thanks again....