I updated the ATI drivers to ver. 8.12 (apparently) succesfully, but still suffer the same problem.
I installed Planeshift from the binaries on the homepage.

This is the relevant (to my mind) part of the output psclient -verbose produces:

VFS_NOTIFY: loaded configuration file: /home/dologan/Planeshift/./vfs.cfg
VFS_NOTIFY: merged configuration file: ./vfs.cfg
NOTIFY: Could not get model converter
NOTIFY: Could not get model crossbuilder
crystalspace.graphics3d.opengl:
  Texture LOD bias -0.3

crystalspace.canvas.glx2d:
  Opening GLX2D
  Creating Context
  Video driver GL/X version (indirect renderer)
  Indirect rendering may indicate a flawed OpenGL setup if you run on a local
  X server.
  Visual ID: 27, 24bit TrueColor
  R8:G8:B8:A8,
  level 0, double buffered

crystalspace.canvas.openglcommon:
  OpenGL renderer: Mesa GLX Indirect (vendor: Mesa project: http://www.mesa3d.org)
  version 1.2 (1.5 Mesa 6.1)
  Using windowed mode at resolution 1024x768.
  Pixel format: Color: 24 Alpha: 8 Depth: 24 Stencil: 8 AccumColor: 24
  AccumAlpha: 8 MultiSamples: 0

ldd on the gl32.so in the Planeshift directory...

        linux-gate.so.1 =>  (0xffffe000)
        libdl.so.2 => /lib32/libdl.so.2 (0x555f7000)
        libnsl.so.1 => /lib32/libnsl.so.1 (0x555fa000)
        libpthread.so.0 => /lib32/libpthread.so.0 (0x5560e000)
        libz.so.1 => /lib32/libz.so.1 (0x55661000)
        libGL.so.1 => /usr/lib32/opengl/ati/lib/libGL.so.1 (0x55672000)
        libSM.so.6 => /usr/lib32/libSM.so.6 (0x5571f000)
        libICE.so.6 => /usr/lib32/libICE.so.6 (0x55728000)
        libX11.so.6 => /usr/lib32/libX11.so.6 (0x5573f000)
        libXext.so.6 => /usr/lib32/libXext.so.6 (0x5580a000)
        libm.so.6 => /lib32/libm.so.6 (0x55819000)
        libstdc++.so.5 => /usr/lib32/libstdc++.so.5 (0x5583b000)
        libgcc_s.so.1 => /lib32/libgcc_s.so.1 (0x558f1000)
        libc.so.6 => /lib32/libc.so.6 (0x558fa000)
        /lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x56555000)