The 20th Amendment doesn't kick in until after December 15th, if not January 6th. There ISN'T a President-Elect OR Vice President-Elect UNTIL THEN.
Referring right now to either Obama/Biden as the "elect" is a misnomer. They are NOT the 'elect' until the ELECTORS CHOOSE THEM in December.
Should Obama be disqualified PRIOR to December 15th or Congress approves their decision on January 6th, it doesn't go to the 20th Amendment as there is NO President or VP-Elect until then.
Understood - assuming Obama is disqualified:
I have some lengthy posts on other threads that explain what could happen before the Electoral College meets and the vote is certified (Obama disqualified, McCain’s electors replace Obama’s, Biden MAYBE getting the VP slot if SCOTUS ruled that his election was legal).
I also detail the scenario after the vote is certified (Obama disqualified, VP Elect becomes acting POTUS on 01/20/09 unti a new POTUS has qualified (which I would believe to be McCain - next highest total from the election). This is where the 20th Amendment kicks in. McCain to be POTUS, Biden MAYBE VP (if SCOTUS ruled that his election was legal).
I also detail what might happen after 10/20/09 (Obama disqualified, Biden assumes POTUS per 25th Amendment and selects VP, McCain suing based on the claim of fraud). Question is at that point - would McCain prevail? If he did, McCain POTUS. Again, Biden MAYBE VP (if SCOTUS ruled that his election was legal).