For feisty, add this line to /etc/apt/sources.list :
     deb     http://dooglus.rincevent.net/synfig/repository/feisty/  ./

   For gutsy, add this line to /etc/apt/sources.list :
     deb     http://dooglus.rincevent.net/synfig/repository/gutsy/   ./

   For hardy, add this line to /etc/apt/sources.list :
     deb     http://dooglus.rincevent.net/synfig/repository/hardy/   ./

   For sid, add this line to /etc/apt/sources.list :
     deb     http://dooglus.rincevent.net/synfig/repository/sid/     ./


   Then:

     sudo apt-get update && sudo apt-get install synfig synfigstudio

   to install.