Recently I found some repositories where to get the GNU Privacy Assistant .deb packages suitable for Xubuntu/Ubuntu 11.10 32 and 64 bit. Maybe GPA is a bit outdate compared to Enigmail, but around there’s still people that like this GTK interface. Below you can find the steps to install it on a 64 or a 32 bit Ubuntu like system.
Xubuntu 64 bit
https://launchpad.net/ubuntu/oneiric/amd64/gpa/0.9.0-1 wget http://launchpadlibrarian.net/37721679/gpa_0.9.0-1_amd64.deb dpkg -i gpa_0.9.0-1_amd64.deb apt-get -f install
Xubuntu 32 bit
https://launchpad.net/ubuntu/oneiric/i386/gpa/0.9.0-1 wget http://launchpadlibrarian.net/37717999/gpa_0.9.0-1_i386.deb dpkg -i gpa_0.9.0-1_i386.deb apt-get -f install
After the installation the GPA can be found in Applications Menu > Accessories > GNU Privacy Assistant.