Start up Terminal.app and type the command
defaults write com.apple.Dashboard devmode YES
and log out and back in again.
Now you can drag Widgets from the Dashboard Dock onto the desktop. You have to use F12 to quit Dashboard while dragging. If you release the mouse after quitting, the Widget remains at the place where you’ve put it as a floating window on top of all others.
To close the Widget, move the mouse over the Widget while holding down the Option key. A “close window” symbol will appear, allowing you to close the Widget.