In the hopes of saving some other poor sot the hours I've spent on this, if you're having problems getting the radeon driver working and you have the following in your /var/log/Xorg.0.log:
(EE) RADEON(0): Kernel modesetting setup faled
You just may be in luck with this solution.
First, download the ports tree if you haven't already.
Next, follow the instructions posted here