Unfortunately, the application ehtray.exe is what is listening for that Green Button push and its always set to launch Media Center. Of course Microsoft did not make it configurable in the registry. My application Intelliremote lets you completely customize all the functions of your remote buttons and includes instructions on disabling the ehtray.exe application forever. I also have a profile for MediaPortal and you can set the Green Button to launch MediaPortal if you wish. Check it out...