Windows Media Player has associated itself with your files. You can change that in preferences in WMP, uncheck what it will play.
You can also change the file association in Windows explorer.
Right click a file and choose Open With..it will give you a list of applications..choose the one you want to use and tick the box to have it open all files of that type with the particular application.
I don't use iTunes, but there is a lot of help on this thread..
http://www.gnutellaforums.com/showth...threadid=36230