if you have the dev tools, the plist editor will do this for you. otherwise, just open the plist up in some text editor, and slog through the XML.
If that isn't your bag, bust out a terminal and type: defaults read com.apple.dock
to see what's in the plist, and then you can apply the many dock hacks with defaults write com.apple.dock xxxxx
where xxxx is the particular hack.
I tried to add settings in the plist, but now typing the command read, I see that by trying to change a command that was not originaly there, I added it. Of course, this setting is not usefull and i'd like to remove it, but how?