http://www.microsoft.com/windows/products/windowsvista/buyorupgrade/activationfaq.mspx
"If you acquired Windows Vista pre-installed on a computer from a major manufacturer (sometimes referred to as an Original Equipment Manufacturer or OEM), Windows Vista will require re-activation if you replace the motherboard with a motherboard not provided by the OEM."
I build it myself with an OEM license, not from a major manufacturer. I don't get all those perqs.
Phil