Testing Kubuntu Dapper Flight 6 on AMD64. On the clean out-of-the-box installation, the X server fails to start. On logging in at the console, Xorg.0.log finishes with:
(WW) ATI: PCI Mach64 in slot 1:0:0 could not be detected!
(WW) ATI: PCI Mach64 in slot 1:0:1 could not be detected!
(EE) No devices detected.
After some research, it seems that the Xserver is selecting the wrong display driver. xorg.conf contains 'Driver "ati"' when apparently it should be 'Driver "radeon"'.
After making this change, the X server will run, but only at a low resolution. Examining Xorg.0.log, it seems that all the higher resolutions are being filtered out because X believes that the monitor's specifications are not compatible with the modes. However this is incorrect; my TFT monitor is being correctly detected - the monitor model name and H sync/V sync values do appear in the log.
However I also noticed in the log references to the secondary monitor port, which I have not connected. It seemed to suggest that the hsync/vsync specifications were being reset to conservative defaults because no DDC monitor was detected.
When I plugged in the secondary monitor connection (actually to the second input on the same TFT monitor as the primary connection) X worked properly and showed full resolution.
Xorg.0.log and xorg.conf files to follow shortly.
xorg.conf on first boot after installation