I'm now running 13.04 and wanted to install some of my favourite themes, but found that the folder .themes was just missing. Does it work to just make the folder?
Create the folder
.themes in your
$HOME if you don't find one.
at least thats where I found mine.
Hope you find this useful.
You can try to install the themes in
/usr/share/themes but you need root. Or you can install them in
~/.themes if that Dir doesn't exist them make it! Also, make sure it is a folder not a file like .zip, .tar, .tar.gz, ect...