I've always assumed that before I can use the Dvorak layout I need to purchase a Dvorak keyboard. But I can't find one on Amazon. Is it simply a matter of popping the keys off a Qwerty keyboard and moving them around?
To help you learn your way around the keyboard layout, you can physically rearrange the keys on your Qwerty keyboard. Or you can simply re-label the keys with stickers. I personally learned to type using the Dvorak layout without re-labeling or re-arranging keys, and found that it was not difficult.
Most modern OSes allow you to remap any keyboard to the Dvorak layout.
Windows XP/Vista: you can set your mappings through Control Panel->Regional and Language Options->Languages->Details....
Mac OSX: System Preferences -> International -> Input Menu (thanks jmah)
Ubuntu: System -> Preferences -> Keyboard, Layouts Tab, Add..., Select the Devorak layout of your choice and optionaly set as default. You can then right-click your panel, select "Add to panel" and choose keyboard indicator. You can then switch between layouts. (Thanks Vagnerr)