In the Leopard dock, any folders become annoying “stacks.” If you want to open the folder, you need to either open the stack and click the “open in Finder” button, cmd+click it and then open the now-selected folder in the Finder, or right click and select “open in Finder.” Any ability to get to a folder with just one click has been removed.
To get around this, you can make an alias of any folder and put that alias on the dock. The alias will now open with just one click.
It will not, however, display its contents as a stack or otherwise do anything other than open or be a drag target. Still, that might be preferable.