Play stuff other than itunes over Airport Express?

I have an airport express that we listen to in the house all the time, but I want to listen to more than just itunes (Pandora, ball games, etc.).

How can this be done? Do I need other equipment? Download software?

Please let me know -
Thanks

This software costs $25 for individual licenses - but they have deals on family packs. It is called airfoil and allows you to play anything from your computer. There is a trial that works for 10 minutes then starts playing noise - good way to tell if it will work for you.
Rogue Amoeba | Airfoil | Select Your Operating System

You can also play anything airplay enabled on an iOS device - Napster and Netflix both are airplay capable.

Thanks - Had heard about airfoil a while ago, but couldn't remember the name and the details.
Thanks for the link - looks like it should work great.
Just don't understand the individual license vs the family pack. It says that the single can be used on multiple machines (same user), while the family pack is multiple machines (different users). I only want it on two (possibly three if we get a new laptop), but could I just be the individual and put them on the different computers? Only one would be playing at a time. Or am I missing something?

1 registered user on 3 computers = single license
3 different registered users on his or hers computer same household =family pack