After some digging I eventually find that the latest FGLRX release has dropped support for HD4xxx and older chipsets! Gee, thanks ATI.
Here's what I've done to pin an older ATI Catalyst driver from snapshot.debian.org:
First step was to find the FGLRX version i needed from the changelogs:
And the date for a compatible X server:
Giving me two lines to add to /etc/apt/sources.list:
#fglrx 12.4.1 pinned from here for now: 4670 not supported after this date
deb http://snapshot.debian.org/archive/debian/20120515T220710Z/ unstable main contrib non-free
#xorg 1.11.2 from as required by fglrx
deb http://snapshot.debian.org/archive/debian/20111201T040728Z/ unstable main contrib non-free
A couple of stanzas are added to /etc/apt/preferences to prioritize the older versions:
(Not complete, room for improvement here)
# fglrx pinned to hold 12.4.1, later versions don't support 4670
Package: *fglrx* xserver-xorg*
Pin: origin "snapshot.debian.org"
#xorg pinned to provide 1.11.2 as required by fglrx
Pin: version 2:188.8.131.521-1
And to accept the older packages I created /etc/apt/apt.conf.d/60ignore_repo_date_check
apt-cache showpkg fglrx-driver will now show the versions available.
apt-get install fglrx-driver=1:12-4-1 installs the desired fglrx version.
apt-get install xserver-xorg=1:7.6+9 installs the corresponding X server
I followed a rather more roundabout route, so YMMV.
After all that fun X works again, but wine 3D performance is abysmal. TF2 is broken, Red Orchestra is 1 FPS and that's all i tested before I gave up in despair.
I chose ATI based on their (AMD's) commitment to releasing the specs required for the development of an OS driver, looks like it is time to revisit that subject, stay tuned...