Not only Bush, but Cheney as well. So, in 2007, you better get used to saying, "President Pelosi."
In our history we've had two Presidential impeachments that went to trial in the Senate, one impeachment attempt that ended with Nixon's resignation, and two vice presidents resigning (one under pressure, one to take a seat in the Senate [John C. Calhoun], when his term as VP was nearly over anyway). The idea that the 'Rats would be able to remove both the President and the Vice President on charges that are only taken seriously by the moonbat base of their party is far-fetched.
And even if they got Cheney and were going after Bush, Bush would be able to name a replacement for Cheney. I don't think the country would stand for Congress refusing to confirm the replacement.