Airport Extreme Wired Network

Turn on the type of sharing you want in Sys Prefs->Sharing.

iTunes sharing is in iTunes->Preferences->Sharing

It can definitely do it. that's how I have my network set up. Should be plug and play.

Have you run the airport utility? If not, do that first. (finder will find it...)

Your other mac should show up in finder window if configured properly.

one quick way to find out where the problem is

get the IP address of your computer
** on mac --system preferences -> network -> connection name (ip will be somewhere on the page 4 numbers seperated by periods probably 10.0.0.## or 192.168.0.#)
** on windows - Right click "network places" -> properties -> select "local area connection" (or whatever your connection is) -> IP is on the left under details or: right click -> status -> support tab

open terminal on a differnet computer
**on a mac - applications -> utilities)
**on windows - start->run-> type "cmd" -> click "ok"

in that window type "ping ##.##.##.##" where the numbers are the ip address you got from the other computer.

it will either give you something that looks like "64 bytes from #.#.#.#: icmp_seq=0 ttl=64 time=0.853 ms" or "host is down"
If the first, your computers can see each other, and the problem is with the file sharing on the computers
if the second, the problem is in your router or network, and for some reason the computers aren't able to talk to each other.