Can I use my phone as an audio device via Wifi?
I have experimented with streaming audio from PC to Android over Bluetooth. Recent versions of BlueZ are able to sink an A2DP stream, but the build I have on my phone (Droid running Sapphire 2.0.2) is outdated and won't do it. You may have better luck.

If that won't work, Android's media player may be able to receive one of the streaming protocols that VLC supports. Another poster may know more about this.