If you mean the windows registry of the client's computer, I can safely tell that that no server side language can do that without some sort of application on the client's machine. Trust me, you do not want websites to be able to read or touch your registry.
No, you can't do that. That would be an enormous security breach. PHP can, however, communicate with some external application that could change your registry, but which you might have to install. Why would you want to do that, anyway?
I have optimistic thoughts, even though sometimes (if not always) life's a bitch.