Insert and boot to the Vista DVD, choose your keyboard/language settings, then on the next screen choose the Repair option from the bottom left corner. If you run the Startup Repair wizard it should resolve the problem, though upon booting Vista you'll likely face an activation warning. That will lead to a short call to Microsoft's toll-free number to have the license validated again. A bit tedious, but with a little luck it will all go smoothly.

Hope this helps,
John


P.S. This assumes there are no SATA drivers needed for the 'new' motherboard.