Gem works but rendering frames is really slow so what i have been doing is setting buffer to 1 and banging gemhead with a metro object so i can set the render rate.
you can either use [declare -stdlib Gem] in your patch or load Gem on startup from File/Preferences/Startup.
if you are having trouble installing pd itself these are the steps i followed to install:
most of this is from the README.txt and INSTALL.txt files in the Pd folder. you can check those files for more information.)
Start by opening a commandline shell:
and entering the following:
sudo apt-get install build-essentials automake autoconf libtool gettext
sudo apt-get install libasound2-dev
then navigate to the Pd source directory:
sudo make install
Additionally I did have to install tcl/tk using:
sudo apt-get install tk
you can then open pd from the command line