You don't really have to do any registering as such. I've seen many programs, like emule, create their own protocol specificier (that's what I think it's called). After that, you basically just have to set some values in the registry as to what program handles that protocol. I'm not sure if there's any official registry of protocol specifiers. There isn't really much to stop you from creating your own protocol specifier for your own application if you want people to open your app from their browser.