If they are the same weapon, when you use the fav menu (on PS3 it is the UP Arrow) the weapons will be bunched (i.e Steel Sword (2) ). You then assign them to reach hand, so when in the menu and the swords are highlighted press the Right Hand Attack (R1 on PS3) to equip one wep there and then press Left Hand Attack (L1 on PS3) to assign that wep to left hand. You can do this if the 1h weps are different as well, just press the hand you want to assign it to's attack button. If you press X (on PS3, use button otherwise) then I think it defaults to the Right Hand for weapons.
To summarise
Equip 1H in Right Hand = Right Hand Attack (R1 on PS3)
Equip 1H in Left Hand = Left Hand Attack (L1 on PS3)
Note: Same with spells as well.
Hope this helps