I think it would depend entirely on what you have in mind. If you want PHP to run winamp on the /server/, considering that winamp is installed on the server OS, then I say it is possible.
As far as the client's browser, well then you're talking about a more complicated undertaking laden with security hurdles that you're unlikely to overcome without client approval. For the sake of argument I'd say that anything is possible given enough effort. Any solution would likely be a mix of more than one language, for instance PHP and Microsoft .NET, or PHP and Java. But anything you want to do on the client's machine is going to be met with security dialouges. You can't just launch software on the client's machine, if you could it'd probably be considered a virus or spyware.
Regards,
Rich
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