according to the writer : This seems to work with iTunes 8 and 9, although you'll need to redo the patch after upgrading.

Open a Terminal and type the following 

    cd /Applications/iTunes.app/Contents/MacOS
    sudo mv iTunes iTunesX
    sudo curl http://www.cs.umd.edu/~dmonner/iTunes -O
    sudo chmod uog+x iTunes enter code here

From http://www.cs.umd.edu/~dmonner/iTunes

    #!/usr/bin/env python
    
    import sys, os, subprocess
    
    launch = True
    blocker = ""
    
    apps = ["Spotify", "Songbird"]
    
    ps = subprocess.Popen("/bin/ps -x", shell=True, stdout=subprocess.PIPE)
    
    for line in ps.stdout.read().split("\n"):
        for app in apps:
            if app in line:
                launch = False
                blocker = app
    
    ps.stdout.close()
    
    if launch :
        os.spawnvp(os.P_WAIT, '/Applications/iTunes.app/Contents/MacOS/iTunesX', sys.argv)
    else :
        print "Not launching iTunes while %s is running." % blocker

and you can read more [here][1] and [here][2].


  [1]: http://discussions.apple.com/thread.jspa?threadID=2122639&start=30&tstart=0
  [2]: http://superuser.com/questions/31925/stop-play-pause-button-opening-itunes-in-snow-leopard