You don't need to install this outdated driver on sid.. You won't be able to compile it for sure. All you need to do is to install this package: http://packages.debian.org/sid/firmware-linux-nonfree via:
#: apt-get install firmware-linux-nonfree
And use opensource driver. By installing nonfree firmware you will enable 3D support for OSS driver. Your card won't be supported anymore by amd driver. They droped it..
If you don't have this package in repos it's possible that you didn't enable non-free repositories in your sources.list. To do so just open /etc/apt/sources.list with your preffered editor and edit these lines:
deb http://ftp.us.debian.org/debian sid main
deb http://ftp.us.debian.org/debian sid main contrib non-free