If you have moved since the last election you need to re-register to be able to vote. Even if you only moved across the street you still need to re- register before you can vote. Obviously, if you have not registered before in order to vote on 11/2/2010 you will need to register.
In California, the dead line for registering is 10/18/2010.
It is easy to register. Simply go here and register on line. Or, you can go to the Registrar of Voters office in your city or county and register there. You may also be able to register at your nearest DMV – good luck on anything happening quickly in there however.