I've downloaded some GTK themes from http://ubuntu-art.org/index.php?xcontentmode=100&PHPSESSID=180c7cef6c965351b9d18e19e3d037e9 and I can't see any instructions on how to install them. For additional information I am running Ubuntu 12.10 Quantal, have Ubuntu Tweak already installed. Thanks for any help!
i guess if it is supported by your desktop you can easily run nautilus with admin rights:
then just go to usr/share/themes folder and unzip files you have downloaded from site.
and install themes via synaptic package manager -just search for themes. https://launchpad.net/~webupd8team/+archive/themes