Equip a weapon in your off-hand to dual wield (you can mix and match any one handed weapons), and put skill points into the dual wielding skill to reduce the off-hand damage penalty (eventually your off-hand will become stronger than your main hand, at level 10).
On the Xbox the off-hand is listed right under the main hand in the equipment list; for the PC I would guess the off-hand equipment slot was either opposite or below the main hand (equip a two handed sword and I would think you should be able to see which other slot is disabled).
