You don’t need to use iTunes to stream audio to an Aiport Express. You can use the Windows Media Player, WinAmp, Rhapsody, etc…
oAEP – Stands for ovesen.NET Airport Express Player. This small application records the music and sound played by your pc and streams it to an Airtunes enabled Airport Express. It has never been this easy streaming music and sound to your Airport Express without using ITunes.
Yes, you red correctly. You can use Media Player, WinAmp or another music player with your Airport Express.
Source included. Neat, this means you can also stream formats iTunes doesn’t, like Ogg Vorbis (well, with a plug-in you can).