[XFCE] How install Window Border themes ?

[alex]

I would like to install a window Border theme from this Gnome website
http://art.gnome.org/themes/metacity/666/

So I extract the tar file
http://art.gnome.org/download/themes/metacity/666/MCity-Litoral.tar.gz
to this directory : /usr/share/xfwm4/themes/

But unfortunately,  I can't see my folder in
panel => setting => Window Manager.

When I rename a  sub directory in /usr/share/xfwm4/themes/, I could see, 
in the Windows Manger, that the sub directory has been renamed.  So I 
thinks it is the good directory /usr/share/xfwm4/themes/ for the 
WindowsBorder Themes.
But why when I put the file metacity-theme-1.xml in the directory 
/usr/share/xfwm4/themes/metacity, it doesn't work ? I can't see metacity 
in the Window manager.