While many have speculated that an official declaration of Obama’s ineligibility may lead to the appointment of Joe Biden as President, the speculation is inaccurate. Since it was up to the respective political party to properly vet their candidate before a primary election, they may not qualify to be rewarded for their lack of integrity. Additionally there is no separate balloting for President and Vice-President; they share the same slot. Obama’s ineligibility would effectively void the entire Obama-Biden ticket.
http://www.michnews.com/Guest_Commentary/Process_for_Ineligible_Elected_Candidate.shtml
Oh and just for giggles it would be decided by the Supreme Court.
The Supreme Court may decide a new election is in order and would have to waive the two-term limitations of George W. Bush so that he can remain in office until the conclusion of the election. The continuation of his term is a viable course of action,
Makes me wonder what Ahmadinejad would do in that scenario. lol.