Wireless Home Audio

Hello,
I am working to get audio from my PC to play through out the house.

I purchased an Apple Airport Express and some computer speakers and have that in the kitchen. It seems to work really well. I have a PlayerPal running on the PC and use my PSP to control the playback functions. However I cant control what AirPort Express is on remotely.

I would like to setup a few more rooms and would like to be able to wireless control the audio playback as well as control what rooms is actually playing (which I cant do right now at all).

I wanted to make sure I exhausted all options before purchasing a few more AirPort Express modules. Obviously I am on a budget and I would really like to use 802.11 wireless not something proprietary.

Thank you for your recommendations.