Do I believe their are alternate universes with alternate us's? No, I believe we are each unique.
Do I believe in multiple universes that are seperate but interact at some level? Yes. To me it only makes sense. I see no reason to limit belief to only 4 dimentions. I have always felt that way. To limit the numbers of dimensions to me would be like putting our universe in a box. There is always something outside the box.
The interesting thing is that there are scientist that now believe that multiple universes are the reason that light acts as both a wave and a particle. Basically it is possible that the light particles are actually bouncing off of the light particles in other universes. Some scientitsts agree, some don't, they all think the one who believes in mulitiple "earths" is a little nuts.