Nope, its fairly disspointing… I would love to also be able to share my iPhone/iPod Touch music with an AirPort express or an Apple TV so I can take advantage of the Wi-Fi capabilities and control my music anywhere in my house…
If you mean tethering, where your computer uses the phone as its internet connection, then no.
But if you jailbreak your phone, you can install a web server on it, and share your music on the local network over HTTP (or even the internet at large, if you have a router and set it up so that port 80 is directed to your iPhone). :)