Here is a handy dandy guide to watching election night. The East Coast states will report first. If John McCain is going to win, then he will win Virginia, North Carolina, and Florida. And then it will take the rest of the night to figure out if he still has enough electoral votes. Obama's victory could be a lot easier to figure out.
If Obama wins Virginia - it's over. That simple. He is comfortably ahead in all of the blue states that John Kerry won in 2004. He is very likely to win all of those. He is also comfortably ahead in Iowa and New Mexico. So, that means all he has to do to get an electoral majority is win Virginia, or Ohio, or Florida, or Colorado. Any of them will do. If McCain wins three out of the four, he still loses.
So, unless something gargantuanly unexpected happens, if they call Virginia for Obama, you will know at that moment that he is the next President of the United States.
Notice North Carolina is not on the list of states that Obama needs. That's because if he wins North Carolina, then he probably won all of those other states anyway and he has blown John McCain out of the water. So, if they call North Carolina for Obama, that's the moment you know that we have a landslide on our hands.
Now, none of this is bound to happen. The polls are just polls, they are not actual votes. That's why they play the games on Sunday (and in this case, do the voting on Tuesday). But this is just a quick guide to watching the game. Virginia equals Obama win. North Carolina equals Obama landslide.