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.