I also don't have dri capability with my Radeon 7000 due to the same problem: undefined symbols.

# export LIBGL_DEBUG=verbose
# glxinfo
name of display: :0.0
libGL: XF86DRIGetClientDriverName: 5.0.3 radeon (screen 0)
libGL: OpenDriver: trying /usr/lib/dri/radeon_dri.so
libGL error: dlopen /usr/lib/dri/radeon_dri.so failed (/usr/lib/dri/radeon_dri.so: undefined symbol: _glapi_get_dispatch)
libGL error: unable to find driver: radeon_dri.so
libGL: XF86DRIGetClientDriverName: 5.0.3 radeon (screen 0)
libGL: OpenDriver: trying /usr/lib/dri/radeon_dri.so
libGL error: dlopen /usr/lib/dri/radeon_dri.so failed (/usr/lib/dri/radeon_dri.so: undefined symbol: _glapi_get_dispatch)
libGL error: unable to find driver: radeon_dri.so
display: :0  screen: 0
direct rendering: No
server glx vendor string: SGI
server glx version string: 1.2
server glx extensions:
    GLX_ARB_multisample, GLX_EXT_visual_info, GLX_EXT_visual_rating,
    GLX_EXT_import_context, GLX_OML_swap_method, GLX_SGI_make_current_read,
    GLX_SGIS_multisample, GLX_SGIX_hyperpipe, GLX_SGIX_swap_barrier,
    GLX_SGIX_fbconfig
client glx vendor string: ATI
client glx version string: 1.3
client glx extensions:
    GLX_EXT_visual_info, GLX_EXT_visual_rating, GLX_EXT_import_context,
    GLX_ARB_get_proc_address, GLX_ARB_multisample, GLX_ATI_pixel_format_float,
    GLX_ATI_render_texture
GLX version: 1.2
GLX extensions:
    GLX_EXT_visual_info, GLX_EXT_visual_rating, GLX_EXT_import_context,
    GLX_ARB_multisample
OpenGL vendor string: Mesa project: www.mesa3d.org
OpenGL renderer string: Mesa GLX Indirect
OpenGL version string: 1.2 (1.5 Mesa 6.4.1)
OpenGL extensions:
    GL_ARB_imaging, GL_ARB_multitexture, GL_ARB_texture_border_clamp,
    GL_ARB_texture_cube_map, GL_ARB_texture_env_add,
    GL_ARB_texture_env_combine, GL_ARB_texture_env_dot3,
    GL_ARB_transpose_matrix, GL_EXT_abgr, GL_EXT_blend_color,
    GL_EXT_blend_minmax, GL_EXT_blend_subtract, GL_EXT_texture_env_add,
    GL_EXT_texture_env_combine, GL_EXT_texture_env_dot3,
    GL_EXT_texture_lod_bias
glu version: 1.3
glu extensions:
    GLU_EXT_nurbs_tessellator, GLU_EXT_object_space_tess

   visual  x  bf lv rg d st colorbuffer ax dp st accumbuffer  ms  cav
 id dep cl sp sz l  ci b ro  r  g  b  a bf th cl  r  g  b  a ns b eat
----------------------------------------------------------------------
0x23 24 tc  0 32  0 r  .  .  8  8  8  8  0 24  0  0  0  0  0  1 0 None
0x24 24 tc  0 32  0 r  .  .  8  8  8  8  0 24  8  0  0  0  0  1 0 None
0x25 24 tc  0 32  0 r  .  .  8  8  8  8  0 24  0 16 16 16 16  1 0 Slow
0x26 24 tc  0 32  0 r  .  .  8  8  8  8  0 24  8 16 16 16 16  1 0 Slow
0x27 24 tc  0 32  0 r  y  .  8  8  8  8  0 24  0  0  0  0  0  1 0 None
0x28 24 tc  0 32  0 r  y  .  8  8  8  8  0 24  8  0  0  0  0  1 0 None
0x29 24 tc  0 32  0 r  y  .  8  8  8  8  0 24  0 16 16 16 16  1 0 Slow
0x2a 24 tc  0 32  0 r  y  .  8  8  8  8  0 24  8 16 16 16 16  1 0 Slow
0x2b 24 dc  0 32  0 r  .  .  8  8  8  8  0 24  0  0  0  0  0  1 0 None
0x2c 24 dc  0 32  0 r  .  .  8  8  8  8  0 24  8  0  0  0  0  1 0 None
0x2d 24 dc  0 32  0 r  .  .  8  8  8  8  0 24  0 16 16 16 16  1 0 Slow
0x2e 24 dc  0 32  0 r  .  .  8  8  8  8  0 24  8 16 16 16 16  1 0 Slow
0x2f 24 dc  0 32  0 r  y  .  8  8  8  8  0 24  0  0  0  0  0  1 0 None
0x30 24 dc  0 32  0 r  y  .  8  8  8  8  0 24  8  0  0  0  0  1 0 None
0x31 24 dc  0 32  0 r  y  .  8  8  8  8  0 24  0 16 16 16 16  1 0 Slow
0x32 24 dc  0 32  0 r  y  .  8  8  8  8  0 24  8 16 16 16 16  1 0 Slow

--

According to this page: http://dri.freedesktop.org/wiki/DriTroubleshooting

...everything is fine in my X11 setup *except* that the dri modules do not match the X11 server, hence the undefined symbol errors. This is a worrying sign that Dapper was not compiled cleanly and correctly.