Software Protect

All,

I am trying to protect my product. So I need to identify user's
machine. I can use Hard disk Serial Number, MAC Address, etc. But for
XP, Microsoft already requires the activation. So I decided simply use
Windows ProductID. What I am wondering is wether the ProductID is unque
or not - especially for Volumn Licensed users.

Also, is there a way to get the Hardware hash?

Thanks

John