RESOLVED: Wired & Wireless in One Network?

I have a Linksys SpeedStream 2614 DSL router (with the ethernet coming from my DSL modem). From the router, I branch off: an Airport Express Base Station (gives my iBook a wireless connection) and a G4 tower. Both computers hop online just fine. Also, both computers can use AirTunes just fine.

I want to share iTunes music and other files between the iBook and the G4. Go >> Network only shows the one computer I'm operating from, not the other computer I wish to connect to. Despite setting up everything to share (both inside iTunes and the System Preferences) and turning AppleTalk on for both machines, they don't see each other unless I physically plug in my iBook to the router. Then, they see each other just fine. But I can't figure out how to keep my G4 wired, my iBook wireless,
and work between both of them.

Any ideas? Thanks.

Whoa! That was much easier than I could have hoped and as easy as I suspected. Here's what was wrong:

The AirPort Express station was distributing IP addresses (AirPort Admin Utility >> Configure >> Network >> uncheck Distribute IP addresses >> click Update).

My router should be the only thing in the network dealing with distributing IP addresses. Otherwise, the network doesn't know where to look for things. It's working perfectly now and I didn't even need to buy an AirPort card for the tower.