I found some new themes on gnomelook.org I am looking for GTK3 themes.But some themes as Zukitwo say that they are for GTK 3.6 but I think mine is GTK 3.4 (I am using Ubuntu 12.04 LTS) so can I use this theme or do I have to find an older version? Thanks in advance.
yes it will work perfectly unless there bug in theme itself here you can see your self http://www.webupd8.org/2012/12/zukitwo-adwaita-cupertino-themes-ported.html