That's not likely though. Basically, if there is a tie in the electoral college, the house picks the president and the senate picks the vice president. So, the senate, which is almost certain to be controlled by the Democrats, would need to pick Palin, which is unlikely.
The house is less certain. Democrats could control is, but the each state gets 1 vote, not each representative. A lot also depends on if a state decides to vote based on the representatives' party or the party that had the most votes from the state vote. Many things could happen and either candidate could end up president if that happens.
But like I said, if it ends up as a tie, I believe is is unlikely that the Senate would pick Palin. Theoretically, it is possible, though.