Gnome is not designed to be minutely configurable. It can be done by editing the XML behind the themes etc. At some stage you will always be limited by the designers choices.
The jpeg you link to looks like fluxbox - though, I think, XFce can be rigged a bit like that.
You can get quite close to that layout gnome. Start with two panels, transparent background, not expanded. Use the tango bluo icons. You are 80% there.
The pull out boxes can be handled using panel draws, which can have a transparent background, and custom icons. I don't think it's a very difficult mod.
For high levels of control, you will be looking for a gui with text-files to edit for everything. E16 is highly configurable like that, so is fluxbox.
The supporters seem to like the level of control you are given.