Bottomline seems to be that the Ubuntu distribution driver must not be there anymore. (So actually this step should not be necessary if I do a fesh Lucid install and DO NOT again trap into the driver-installer-applet before trying the scripted installer from AMD.
No problem then, I made it a custom to completely try any Ubuntu on a stick drive, and only install it on HD if I am sure that everything works. ...because unfortunately Ubuntu gets worse and worse with each release. Yes they add more features, but the original 'Ubuntu-Effect' (Ahh, a Linux where everything works ootb) is certainy tainted nowandays.
Anyway, I did not change the color depth.
Will try all this later. xorg.conf would be appreciated.