Hello LeahW,
The support page that asks for your PID states:
"To determine if no-charge support is available, provide the product identification number". It gives you an error of "Invalid" because your copy of Vista does not qualify for no-charge support. You can click the "Skip to payment" button if you wish to use Microsoft's Pay for Support service.
The reason your Vista does not qualify for No-charge support is because your Vista came Pre-installed on a computer built by a large computer manufacturer (such as Dell, HP..so on) These companies pay a lower price for Windows and in exchange they take over responability for all warrenty support for the Windows that they sell pre-installed on their computers.
Example: Say you have a Dell computer and the DVD drive (that was manufactured by Sony) stops working. You would go to Dell for warrenty support to fix the DVD drive, not Sony. Windows is a component of the computer, just as the DVD drive is.
Thank you,
Darin Smith
WGA Forum Manager