If you like the new 3-D dock in Leopard, good for you. If you don't you have a couple of options that will allow you to have a more familiar and less-flashy 2-D dock.

First, you can drag the dock to either side of the screen. When the dock is on the side, it reverts to a 2-D dock. You can check it out pretty easily this way to figure out which type of dock you prefer. Just move the dock back to the bottom of the screen and you'll have a 3-D dock again.

If you decide you prefer the 2-D dock, but you want it on the bottom of the screen and not on the sides, this can be done easily. Just open a terminal window (finally, with tabs!) and type the following:

defaults write com.apple.dock no-glass -boolean YES; killall Dock

If you want to revert back to the 3-D dock, you can repeat the command and change the YES to a NO.