To kill the dock in Mac OS X, in a Terminal, type:

killall Dock

The dock will shut down and  re-start automatically.  If do not want the dock to run at all—for example if you want to free up memory or free up pixels from the screen—remove the /System/Library/CoreServices/Dock.app directory with:

cd /System/Library/CoreServices
sudo mv Dock.app Dock.app.orig
killall Dock

Removing the Dock.app directory causes the dock to stay dead after you shut it down.  This will also disable the command-tab window switcher and the background image on the desktop.

To undo the change, restore the Dock.app directory with:

cd /System/Library/CoreServices
sudo mv Dock.app.orig Dock.app

The dock will restart up automatically.