FFIV Minisode Episode 3 - Weapon Duplication Glitch
This video details how to pull of the Weapon Duplication Glitch, which is different than the Infinite Weapons Glitch.
This glitch is rather simple to do. All you need to do is, when in battle, go into your Item menu, select a blank slot, and unequip anything in that character's hand and finish the battle (can be done with all characters). This can mean winning the fight or running away, matters not. Next, go into the Equip menu of that character, then equip any weapon or shield in that character's hand of which you put the blank slot on. You should see a 2 next to that weapon/shield. Unequip it, and you should now have 2 of that weapon/shield instead of 1. Simple as that!