In 3rd edition, if your opponent is denied their dexterity bonus for whatever reason, or they are flanked, a rogue can sneak attack with as many attacks as he has each round. This is true whether it is with secondary attacks or off-hand attacks.
Items do not have damage reduction, they have hardness. Hardness reduces damage right off the top. Only damage dealt in excess of the hardness is applied to the object's hitpoints. Energy based attacks affect items differently as well, here's a quote from the SRD:
Some materials may have particular weaknesses though and this is left mostly to the DMs discretion. The players handbook (pg 165) gives the example that a curtain may be especially easy to light on fire, or it may be easy to chop down a tree with an axe. In those cases, the attack deals double damage and may possibly ignore the object's hardness altogether.Acid and sonic attacks deal damage to most objects just as they do to creatures; roll damage and apply it normally after a successful hit. Electricity and fire attacks deal half damage to most objects; divide the damage dealt by 2 before applying the hardness. Cold attacks deal one-quarter damage to most objects; divide the damage dealt by 4 before applying the hardness.