If the election proved fraudulent by Obama; neither Obama nor Biden would have any role. Since the election would not have been decided; I would believe George W would still be POTUS regardless of his term ending the usual way. In this case; it would not be the usual way.
And how to you reconcile that odd-ball solution with the 22nd Amendment?
No - the Vice President is a separate office. Electors vote for President and Vice President separately.
Biden is eligible for the office since he is a NBC. If for any reason, at this point that Obama can not serve or is removed, then Biden becomes President.
To remove Biden as President would require that he be impeached by Congress.
Your belief would somehow be in conflict with the following or would it not?
http://www.law.cornell.edu/constitution/constitution.amendmentxx.html