Ubuntu – How to install Emerald Theme Manager, and switch between Emerald and Metacity themes

To use emerald on 11.04:

Remove Emerald:

$ sudo apt-get purge emerald

Deps:

$ sudo apt-get install libwnck-dev libwnck1.0-cil-dev git automake libtool intltool libdecoration0 libdecoration0-dev

Compile:

git clone git://anongit.compiz.org/fusion/decorators/emerald
cd emerald
git checkout -b compiz++ origin/compiz++
./autogen.sh
./configure --prefix=/usr/local
make && sudo make install

Now, open CompizConfig and enable "Window Decoration", "Resize Window" and "Move Window". Make sure "Window Decoration"'s command is emerald --replace .

Press alt+f2 to run this command:

emerald --replace

You should now have your emerald theme activated and have the ability to move the windows around. :D

11.10 Edits

You may have to modify the directions above slightly:

Compile:

git clone git://anongit.compiz.org/fusion/decorators/emerald
cd emerald
git checkout -b compiz++ origin/compiz++
git reset --hard 0936b42efbc4247d1af16d5043f9a7a36ed8063a
./autogen.sh
./configure --prefix=/usr/local
make && sudo make install

Note: The git reset command goes to a specific release of their code. It seems the latest version is broken, but this is subject to change. You may want to attempt the original instructions, and revert back to commit 0936b42efbc4247d1af16d5043f9a7a36ed8063a only if you are unable to compile Emerald.

What you are referring to as a theme is probably a different kind of theme (in light of your comment on Uri's answer).

Those themes control GTK, Metacity (the Gnome 2 windows manager), Icons, cursors, and sometimes wallpapers all in one. However, they do not control your emerald theme. What you are seeing referred to as a GTK, Metacity, Cursor, or Icon theme is what you get when you click customize.
Each of these controls a different aspect of your interface, and of course, they are all themes in their own right.