There is a program called SkinMobile that will allow you to skin the taskbar. The desired effect can be accomplished by using the same background image to create the skin. The program is a little glitchy, but essentially it does the job and it's fun to play with. You should be able to find it with a search, if not I'll upload later. Here is an example of an UltimateLaunch theme I was running back in the day using SkinMobile to complete the effect.
You might look into VJTodayToggle and/or dcinobar as additional taskbar and bottom bar hiding utilities. [Edit: I believe no2chem also made a bottom bar hiding utility that worked correctly with the newer WM builds. The above should get you started, if you need specifics post a reply
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