I have an Sapphire HD4870 works great with latest closed src driver but the video driver locks up when using 6.12.2 open src driver.
The lock up occurs always when the windowmanager first maps the screen when the server starts up.
System is running debian testing with the apropriate packages hand installed from unstable.

Note: the kernel and everything else runs OK only the keyboard and video do not function.

Is there anything required in the xorg.conf file for this.

When the OS driver was tried the closed src was completely removed to stop it interfereing.