You then have to apply a patch to the kernel, a patch to mesa master, regular old libdrm master (without any patches now that they're merged), and a patch to the DDX. DDX shouldn't need a patch before long, and it'll probably hit mesa master eventually too. Once it does, the only patch you'll need is the kernel until 3.4-rc is out.
0001-drm-* = for kernel, will be in mainline by linux 3.4-rc1
0001-r600-* = for DDX (xf86-video-ati), will be applied to master soon (?)
0001-r600g-* = for mesa gallium3d, will be applied to master no later than when they branch for mesa 8.1
0001-radeon-* = for libdrm, but currently all of these are merged to master so don't download or apply them
To "apply" them, just use
git apply 0001-whatever.patch
in the top directory of the sources. Then build like you normally would build from source, out of the scope of this mini-howto.