airport express setup assistant software?

Hey, all. A friend of mine gave me her airport express and I want to use it to stream music from iTunes to my living room stereo. Unfortunately, she can't find the CD that came with it and I'm a bit of newbie when it comes to Apple products. I downloaded the user guide, but it says to use the AirPort Setup Assistant and I can't figure out how to download it. Can somoene point me in the right direction?

Any other tips on setting up an AirPort for use with a Windows XP based PC would be much appreciated as well. I have a wireless network setup with a Zyxel router already, should that matter.

Thanks in advance for your help.