The procedure to copy items in Divine Divinity follows, but I'm pretty sure they fixed that exploit in Beyond Divinity.
In DD, to copy an item; quick save the game, then drag an item out of your inventory, but not somewhere there is a red X. Without dropping first, quick load the game, then release the mouse button when it starts to load. This will produce a copy of the item on the ground, with the original still in your inventory.
There are other cheats and exploits in BD, though.
For you cheaters out there (The Duplication Trick)armory trick in act 1Hex editing - gold, experience, stat/skill points