When in the voting booth tomorrow voting for President, you'll actually be voting for a group of people, none of which are running for President. Casting your vote for Obama, McCain, or any of the other candidates is actually casting your vote for a group of people who represent the candidate's party. They are called electors. Look closely at the ballot tomorrow. It states that you are voting for "Electors of President of the United States," not just for the President of the United States. These electors (538 total in the U.S., including 3 from DC) are the actual people who vote to determine the President of the United States. Each party chooses it's electors in a different manner, which also varies by state.
You may remember that in the 2004 election, the final electoral count was 286 for Bush, 251 for Kerry, and 1 for Edwards. John Edwards actually got an electoral vote for President of the United States from an elector in Minnesota. That incident got me interested in the whole electoral process again.
A candidate needs a plurality of electors, at least 270, to vote for him or her to claim the Presidency. The real vote for President in 2008 happens on December 15, 2008. That day the electors in each state and the District of Columbia will gather in their respective state capitals and officially cast their votes. The vote counts will be sealed and sent to the United States Congress. They will be unsealed and read allowed on the floor of a joint session of Congress next January 6, 2009. There will be a new Congress in session at that point, including newly elected members from the November 4 elections. Only after that reading will the President elect be officially declared the next President of the United States, inaugurated two weeks later on January 20th 2009.
Interesting system. The reasons behind its creation go all the way back to the nation's founding and are fairly complicated. There are federal and state laws that govern every aspect from whether or not an elector can vote for a candidate which didn't win their respective state (some states outlaw it, others don't) to setting up a possibility of having a candidate win the popular vote, but lose the election (has happened three times in U.S. history). If you'd like to read more, there's a great concise and easy to read book called After the People Vote.