I have added 32bit support and installed additional stuff through terminal.. and it still won't run.. I have AMD X4 620 and Radeon 6950 2gb.
The output of running it from the command line:
Running Steam on ubuntu 15.04 64-bit STEAM_RUNTIME is enabled automatically
Installing breakpad exception handler for appid(steam)/version(1428965940)
libGL error: unable to load driver: r600_dri.so
libGL error: driver pointer missing
libGL error: failed to load driver: r600
libGL error: unable to load driver: swrast_dri.so
libGL error: failed to load driver: swrast