Perhaps this is nothing and it just stems from my lack of knowledge, but I saw that the output of your uname -a command yielded:
Linux imladris 2.6.32-trunk-amd64 #1 SMP Sun Jan 10 22:40:40 UTC 2010 x86_64 GNU/Linux Kernel 2.6.32-trunk was removed from sid a while ago. You should have the latest: http://packages.debian.org/sid/linux-image-2.6.32-4-amd64. This last one has many bugfixes for enable KMS with radeon. Let me know what happens Andres
