As stated at page 50 of the player's handbook at the paragraph about sneak attack ,the rogue's attack deals extra damage any time her target would be denied a dex bonus to AC, or when the rogue flanks the target.
So ,you can sneak attack with each one of your attacks when using two-weapon fighting
-provided that the target is denied his dex bonus to armor class or you have flanked him.
Welcome to the boards, and happy sneak-attacking!!!
_________________
The Wizard