In the future, pay attention to programs when they install. Generally every media player I have seen has a "Use me as default" on install, including iTunes. It's easier to catch this on install then it is later.

To disable iTunes from reclaiming music files, go to Edit - Preferences and uncheck "Use iTunes as the default player".

As for the iPod stuff follow the service instructions above. The one you want to disable is "iPod Service". Doing so stops the iPod part of iTunes from working, but lets everything else work fine.

I personally have nothing against iTunes, as it is just as good/bad as most other players like WinAMP on how it behaves. I personally use it to listen to several internet radio stations. My empeg or Rio Receiver provide access to my personal music.