Can't install new themes

[Ari Torhamo]

Hello,

I've been trying for a while now to install new themes to Hoary, but
without success. There seems to be something wrong with the  process (or
I'm badly missing something obvious). It should be straight forward -
from the User Guide:
..............
You can add a theme to the list of available themes. The new theme must
be an archive file that is tarred and zipped. That is, the new theme
must be a .tar.gz file.

To install a new theme, perform the following steps:

     1. Start the Theme preference tool. 
     2. Click on the Install Theme button. A Theme Installation dialog
        is displayed. 
     3. Enter the location of the theme archive file in the drop-down
        combination box. Alternatively, to browse for the file, click on
        the Browse button. When you have selected the file, click OK. 
     4. Click on the Install button to install the new theme.  
..............

I can see in Synaptic that I have for example the package
gtk2-engines-mist already installed in my system, but I can't find
any .tar.gz files belonging to this theme anywhere. If I go
to /usr/share/themes/Mist, theres just one folder, gtk-2.0, that
includes just one file, gtkrc. This file isn't a .tar.gz and the theme
installation tool doesn't accept it saying "Wrong file format". The tool
doesn't accept any other files belonging to Mist either.

I tried the same with gtk2-engines-crux too, but had no more success
there. So what am I missing here? I like to change theme every now and
then to match my mood, but it would be nice to have a few more themes to
choose from.

Thanks,

Ari