I've done a fresh install of Ubuntu 12.10 on my machine which has an AMD4890 video card. As I have come to find out, legacy card drivers no longer work with Xorg in 12.10. I have found many recommendations for this procedure: https://launchpad.net/~makson96/+archive/fglrx
However, when I follow this step by step, I still get no unity after the reboot.