If you are like me, one reason you switched to Linux is for customization.  In the past I ran Gentoo where every bleeding edge package was available to me.  So I was always trying out new and cool GTK engines as they came out.  But on Ubuntu, you don't get that luxury all the time.  So, I will show you how to get two of the latest engines available, Murrine and Candido, on your spiffy Ubuntu machine.

What is a GTK Engine?

For a little background, a GTK engine is what drives the look and feel of the apps on your Gnome desktop.  This includes what some people think of as the desktop itself - the filesystem browser, Nautilus, and the panels, gnome-panel. 

And here you thought the theme was the only thing that mattered.  The GTK engine is like a house, and a GTK theme is the paint on the house.  You can make the house look different ways with the paint, but in the end it still is the same house underneath.  And a good paint job can only do so much. 

The engine can have a drastic effect on the performance, making Gnome feel snappy under some, and sluggish when using others.  So, it's pretty important to the look of your desktop, even though most of us forget it is even there. 

Murrine and Candido

Recently, two new engines, Murrine and Candido have been developed by a talented Italian hacker named Cimitan Andrea.  I've found them to be extremely high performance, and the themes built on them look very nice.  But, they aren't available on Ubuntu Edgy (update: reported in comments below, Fiesty has Murrine as gtk2-engines-murrine, but Fiesy does not have Candido.  Thanks Christer).

Installing Murrine on Ubuntu

First, if you don't already have it, you need build-essential to do these installs, because we are installing from source.

sudo apt-get install build-essential

Download Murrine from Cimi's website here.  Cimi offers .deb files, but they are pretty old.  I suggest getting the Source package.  To find the latest release, you need to be aware that the numbers go 0.1, 0.2, 0.3, 0.4...0.10, 0.11...0.20, 0.30, and so on.  In other words, 0.10 is newer than 0.9.  The newest at the time I'm writing is murrine-0.51.tar.bz2.

Extract the latest version to a folder anywhere (your desktop should do).  Open up a terminal window, and cd until you get to the directory that was created during the extraction, murrine-0.xx.

./configure --prefix=/usr --enable-animation
make
sudo make install

That's really all there is to it, except you probably want some themes.  The best place I've found is gnome-look.org.  Once there, use the search box in the right margin of the page, and search for "Murrina".  Note, the engine is named Murrine, because it is plural in Italian, but the themes all start with Murrina, which is singular in Italian.

Installing Candido

Candido's install is very similar.  Download the latest version here, using the package that says Source Code.  Again, 0.9.10 is a newer version than 0.9.9, and 0.10.0 is even newer than that.  The latest version at the time of this writing is candido-engine-0.9.1.tar.bz2.  And again, you could download the .deb, but it's not always the latest version, and you can't use it on non-x86 architectures like AMD64, so I'm going to explain the source install. 

Extract the latest version to a folder anywhere (your desktop should do).  Open up a terminal window, and cd until you get to the directory that was created during the extraction, candido-engine-x.x.x.  Then run these commands:

./configure --prefix=/usr --enable-animation
make
sudo make install

Again, that's all there was to it, but you need some themes.  There's quite a bit of themes on the project  theme page.  Also, if you go to gnome-look.org again and search for Candido, you'll find several there.

Here's some of what you'll get to see.  Please note, these are only select themes.  Both engines have a variety of themes from light to dark.
 

Candido

Murrine