After a discussion on a bug in the Xorg and ATI graphics card, I installed Google Earth to check that my graphics card is actually functioning correctly. My graphics card is the RADEON Mobility 9000 with the following Xorg.0.log:
(II) RADEON(0): [agp] GART texture map handle = 0xb0302000
(II) RADEON(0): [agp] GART Texture map mapped at 0xb51da000
(II) [...]