"audiogalaxy" app does this. I believe your computer has to be running to access it though; I have trouble connecting on the road if my mac sleeps at home.
I hooked up gmote - worked great over wi-fi. Tonight I set up port forwarding as per the directions on the gmote site and voila! It SEEMS to be work when I open the app on my phone and choose Find Server, my server was listed. I clicked on it and once again it worked. Hopefully I'll be listening to Jon Anderson's Survival while cruising down Rt 78.
So far gmote is working over wifi but once I get out of range it drops and it can't find my server either by the IP. will have to play around a little more.
I have never had a problem with audiogalaxy over wifi or 3g. Listen every day on my way to work and I have a terabyte external hard drive on my computer.