In order to duel wield you need to select the off-hand in your inventory (by the character model), hit A and then select the weapon you wish to use (just equipping a weapon defaults to the main hand). There is no problem mixing types of one handed weapons (in the inventory the average damage of both weapons will be shown). Until you raise the Duel Wielding Expertise skill your off-hand will receive a penalty, so at the start of the game the bonuses on the weapon may be more important than the straight damage value.
Welcome to the forum.
