One item in the volume activation step by step guide that is a bit confusing is the method for moving a Vista machine that is currently using the MAK back to being a KMS client.
The instructions are easy to follow, you use slmgr.vbs and the extensions "-ipk <setup key>". No problem! Wait. Setup key?
If you search the document for pid.txt you will find a section titled Product Key Considerations. In the section the paragraph contains:
"Volume editions of Windows Vista default to KMS-based activation and do not require a product key to be entered during setup. Windows Vista Volume License editions use a specific pre-defined setup key in the sources\pid.txt file."
That is the setup key referenced by the example. So if you open .\Sources\pid.txt on your Vista volume media, you will find a generic product key that is used for your installations by default. That key tells the machine to become a KMS client, and is what should be used in the operation where <setup key> is given. You can use it for any of the volume media installations where you were using MAK and want to convert back to being a KMS client.