It's not necessary to be born in the US; it's necessary to be a "natural born citizen" or a citizen of the US at the time the Constitution was adopted. John McCain was born a US citizen, but he was born in the Panama Canal Zone, and he's running for President in 2008. Barry Goldwater was born in Arizona, but Arizona was not a state in 1909. I can safely state that no one alive in 1787 is alive today, so there's no possibility short of a constitutional amendment for any naturalized citizen to be elected President.
You might be eligible if you’re born on foreign soil and your parents are US citizens. Not sure. However, the Panama Canal Zone was a US territory at that time.