This is not an official binary distribution of stepmania.  It is built for amd64 debian, and if it works at all for you, it should be considered luck.
This is "whatever Kyzentun is running".  At the moment that means it has everything beta 4 has.
Before resorting to using this, try to build from source.  You need the files include with the stepmania source to use this anyway.

The .so files in this folder belong in different places, and have to be moved there by hand to work.
I might have the library names slightly wrong.  If you try to run stepmania, and it says "cannot find libavformat.so", and this folder contains "libavformat.so.55", rename it to "libavformat.so".
If there is already a libGLEW.so.1.5.4 file in /usr/lib, do not replace it with the one in this folder.

GTKModule.so belongs in the stepmania folder, the same folder that has autogen.sh and the other things needed to build stepmania from source.
libGLEW.so.1.5.4 belongs in /usr/lib/
libavcodec.so.55 belongs in stepmania/bundle/ffmpeg/libavcodec/
libavformat.so.55 belongs in stepmania/bundle/ffmpeg/libavformat/
libavutil.so.52 belongs in stepmania/bundle/ffmpeg/libavutil/
libswscale.so.2 belongs in stepmania/bundle/ffmpeg/libswscale/
stepmania belongs in the stepmania folder, the same place as GTKModule.so.

stepmania is the executable, run it to play stepmania.