How can I configure AX to only stream music?

Question

My set-up: G4 tower running OS X 10.4.11 with an early AirPort card installed (probably 801.11b) and a used AirPort Express (AX) 801.11g. For my internet and printer network I have an ethernet D-Link router whose 4 ports are all in use. I intend to keep that network for my DSL and printer. All I got the AX for was to stream music to my stereo from my Mac.
Problem: I've been unable to get my Mac to "see" AX as a wireless device. I have it plugged into a power-strip across the room near the stereo with an audio cord to my stereo plugged into it.
Under another topic on this forum it was suggested that I configure the AX by directly connecting to it with an ethernet chord from it to my Mac. I did this, but much of the configuring process seemed to be for setting it up as an Internet router, which I don't want it to be. And anyway, after I configured it and unplugged it from the ethernet and plugged it in across the room again, the Mac still couldn't see it.
It was also suggested that I set it up as a bridge on the existing D-Link network by connecting the AX to the router via ethernet, but this won't work because 1) all the D-Link ports are already in use, and 2) the D-Link is across the room from the AX near my computer and I don't need one more big honking cable strung across the room.
All I want to do is make the streaming music set-up shown in the diagram on page 18 of the AirPort Express Setup Guide 5.1 work as shown. That's all. I'm on my second day of pounding away on this (it has used up probably a good 6 hours of my time already).
Any help would be appreciated, especially from anyone who has run into precisely this same problem and successfully solved it. If you need more details from me, I'll provide them as I can.

Answer 1

I think that it is beginning to dawn on me that I've been thinking of the whole Airport Express model in the wrong way. I had it in my mind that you plugged in Airport Express, ran an audio cable between it and your stereo, and via the Airport card in your Mac you could transmit music from iTunes to your stereo as if Airport Express were some kind of in-between receiver/transmitter.
But, I'm now thinking that that is not the right paradigm. What one really has with Airport Express is a wireless network router which has the incidental capacity to receive music from iTunes and pass it along to your stereo.
In other words, in configuring Airport Express, what I am really doing is creating a wireless network. If you already have a wireless network in place, then the Airport Express just acts as an extension of that, and the music can be transmitted via the network from one of the computers on it to the stereo wired into the Airport Express.
Or, if you don't have a wireless network in place, you can create one in configuring the Airport Express.
BUT, if you have an ethernet network in place (as do I) then you run into the knotty issue that in configuring Airport Express you are creating an additional network. So, even if I get my Mac to "see" the Airport Express network (which remains hypothetical after 2 days), it seems probable that I'll have to 'turn off' my ethernet network when I want to pipe music through the AE network, because it seems unlikely that I can run an ethernet AND a wireless network both at the same time.
This could be solved, from what I am beginning to comprehend, by hard wiring the AE via an ethernet cable into my D-Link router, except that 1) my D-Link's ports are all already full, and 2) my D-Link is near my Mac and the stereo is across the room and the cable between the stereo and the AE is only 6 feet long. And if I were to string an ethernet cable all the way to the AE, I might as well just run a stereo cable all the way across the room between the Mac and stereo and skip the Airport Express altogether.
I could possibly solve all this by ditching the D-Link ethernet network altogether and going all wireless, but I have little faith that the single Airport Express would have sufficient range to reach my wife's PC laptop in the living room. I suppose, if I were really brave, I might test this out by trying to swap our working ethernet DSL and printer network over to wireless on the AE and see if her laptop could pick up the Airport Express from my study, but I suspect it might not AND we would still have the 'across the room' issue, as I would have to run an ethernet DSL cable from the DSL modem near my computer to the AE near the stereo.
So I think this is one of those "can't get there from here" situations. I did notice that the latest (early 2008) version of the Airport Express Setup Guide has eliminated the diagram showing a Mac transmitting to AE with audio cable to stereo. Perhaps Apple realized that touting AE as a connection for a printer or for music alone was misleading as it would conflict with another network already in place, unless one made the AE a bridge from that network.
If someone can debunk these hard-won conclusions and show me a way to keep my ethernet network intact while simultaneously running an AE network to just my stereo, you are welcome to.