If you drag onto a minimised dock, it will expand for the duration of the drag and shrink again afterwards. The position of the minimised window is remembered separately from the normal dock position so, for example, you can have a minimised dock at the very bottom of your screen that moves upwards to reveal the full dock. Just drag around the minimised dock to where you want it to be.
To make a dock automatically minimise when you switch to a different application (for example, when you double-click an item), set the option "Minimise in background" in the Dock Options window described below. To make the dock automatically maximise when DragThing is brought to the front, set the other option "Maximise in foreground".