It looks like you might have iTunes set to "Copy files to iTunes Music folder when adding to library" You should check around to make sure you didn't accidentally duplicate your entire iTunes library
Do you have firewall turned on in system preferences? turn it off, if you do. Are you using "connect to server" from finder to connect to your file server? You'll have to use (assuming it is an smb share) SMB://addressofserver/foldername. If you want to set up a good file server, I would set...
are you on a mac or pc? i'm guessing mac, if so...
I haven't figured out a way to use static IPs with the router, but on each individual node you can use a static IP. If you only stay on one wireless network, you can use a setting in System Preferences>Network>Airport>TCP/IP and confingure...
I was looking for the answer to this problem myself, and came across this thread. I managed to get this working, so I thought i'd post my $.02
Follow Mikuro's directions here:
Then, under the Airport tab choose "Base Station Options" and put a check in the box by "Enable NAT Port Mapping...