Unverified. To duplicate items after downloading Xbox 360 Shivering Isles expansion pack do the following:
1. Equip a Scroll that you have multiple of (for example, Minor Heal Other x10). If you have ten scrolls you will get ten items.
2. Swing a weapon, and before the animation is over go to your inventory.
3. Select the equipped scroll and press GREEN twice (you won't get a message)
4. Drop the item you want to be duplicated. Note: you can only duplicate things that you have less than the amount of scrolls you equipped. So for example with ten scrolls, you cannot duplicate a potion where you have eleven bottles of. To get around this just drop a few of the items you want to duplicate before you start this glitch so you have fewer items than the amount of scrolls that you have.
Hint - Double Duke Achievement:
When Sheogorath tells you that you need to replace a Duke, save your game before committing to the quest. Accept and complete one of the Duke quests.
Once the other Duke comes storming in, you will get either the Duke of Mania or Duke of Dementia achievement.
At that point, reload the game to when Sheogorath is awaiting your quest decision. Do the other quest and continue playing the game for both achievements easily.