Airport Express for Streaming Music - wrong device?

I think I bought the wrong device. I have a non-apple wireless network, and I want to use the airport express to stream music as a wireless device connected to a stereo in a remote location of the house. Somehow I thought the airport express could join my existing wireless network act as a wireless receiver sending music to the stereo. After reading the install instructions, it looks like I must have the airport express connected to the network via ethernet cable to stream music to the stereo. Crap, I dont want to wire the house.

Is this the way the device works or do I have my wires crossed?

No, it's OK. You can do exactly what you want - unless something has changed on the newest version.

You should just be able to have the Express join your existing network then run the 3.5mm cable from the express to the stereo.

Have a non-Apple network is no problem. You only need to have an Apple router or another Express if your extending the network.

Have a look here:
http://support.apple.com/kb/HT4587

The scenario you describe is "Connecting to an existing Wi-Fi network, exclusively for iTunes music"

I use an airport express to stream music, even before I upgraded my old router to an Airport Extreme. I am not at home, so I can't easily walk through the settings, but make sure you can see the Airport express on the network first. Then, bring up the utility for the airport express (Airport Utility on OSX/iOS) and go to the AirPlay tab and check Enable Airplay and enter the speaker name and the airplay password. If you have Home Sharing enabled anywhere, use the same password.

Great - thanks! I will setup it up and give it a go.