Save yourself the bother and just read the synopsis for the first game all you'll miss is some details about the pieces of eden and what the templars are up to.
The second game has different characters from the first and expands upon the background story but can easily be played without playing the first. I played the first but never finished it due it being too repetitive - locate person,pickpocket,assasinate repeat ad nausuem, I lost interest halfway through. It didn't spoil my enjoyment of the second game which is much more varied.
Oh and on topic an AC:Botherhood producer is saying WW2 is a possible setting for AC3. Personally I don't want to see WW2 it's to modern (relatively speaking!)