I would strongly advise against hunting and pecking. Print out the Dvorak layout and place it next to your computer, put your fingers on the home row, and type. Doesn't matter how slowly---it's important to make the correct finger press the correct key. Don't switch back and forth between QWERTY and Dvorak, you'll learn best if you do it in an immersive way.

Personally I think that a print out next to your screen is a better idea than any cover, because you want to break the habit of looking where you are typing.