Thanks, installing the proprietary ATI once again fixed it (but "apt-get upgrade" doesn't help... had to a "apt-get install xserver-xorg-core=2:1.6.0-0ubuntu14 xserver-common=2:1.6.0-0ubuntu14" to get the original X-Server versions back).
So I have a running 3D Desktop now, that takes 1 to 3 seconds (while playing music stops) to resize a simple window... :-/ I hope, that these issues are fixed soon for every 3D-card.
Thanks, installing the proprietary ATI once again fixed it (but "apt-get upgrade" doesn't help... had to a "apt-get install xserver- xorg-core= 2:1.6.0- 0ubuntu14 xserver- common= 2:1.6.0- 0ubuntu14" to get the original X-Server versions back).
So I have a running 3D Desktop now, that takes 1 to 3 seconds (while playing music stops) to resize a simple window... :-/ I hope, that these issues are fixed soon for every 3D-card.