adding wired computer to network



I'm attempting to add a wired Mac to my existing wireless network, and having some problems.

My DSL line comes through a Zyxel modem, which is connected to a Linksys router that is connected via Ethernet to an Airport Express. One more Airport Express is connected to my living room stereo. I've been running my MacBook laptop off of the wireless with no problems.

What I'm trying to do now is connect a desktop Mac tower to the network via another ethernet connection to a third Airport Express unit. This desktop was previously on the network through a direct ethernet connection to the router. I'm running two external hard drives through the tower, with the end in mind of accessing both these drives from the wireless laptop.

I've tried reconfiguring the third Airport Express unit in line with advice on the Apple Support Forums -- setting it up as WDS as well as in Bridge mode -- but I've gotten a bit lost along the way.

Any advice would, of course, be much appreciated.

Much obliged,