I assume you are installing from openssn-1.3.tar.gz. The README is pretty cryptic about what's needed, since it assumes you are a bit experienced and you might be compiling for any number of Linux distributions. A bit by trial and error, I got it to 'make' without error or warning by installing from Synaptic: libsdl-mixer1.2, libsdl-ttf2.0-0, libsmpeg0,sdlbasic, sdlbrt, libasound2-dev, libavahi-client-dev,
libavahi-common-dev, libcaca-dev, libdbus-1-dev, libdrm-dev, libgl1-mesa-dev, libglu1-mesa-dev,libpulse-dev, libsdl1.2-dev, libslang2-dev, libx11-xcb-dev,
libxcb-glx0-dev, libxdamage-dev, libxfixes-dev, libxxf86vm-dev, mesa-common-dev, x11proto-damage-dev, x11proto-dri2-dev,x11proto-fixes-dev, x11proto-gl-dev, x11proto-xf86vidmode-dev, libsdl-gfx1.2-4, libsdl-gfx1.2-dev, libsdl-image1.2-dev, gnu-smalltalk, gnu-smalltalk-common, libgst7, libmikmod2-dev, libsdl-mixer-gst, libsdl-mixer1.2-dev and libsigsegv2.
I built it on 12.10, so some details may differ slightly.
Good luck and have fun!