Downloaded and installed this one. First I supposed the driver to be the 12-12beta driver (now i am not shure about this):

Latest Beta Driver 109.4 MB 12.11 Beta 12/3/2012

... and inside:

fglrxinfo shows:
display: :0  screen: 0
OpenGL vendor string: Advanced Micro Devices, Inc.
OpenGL renderer string: AMD Radeon HD 7700 Series 
OpenGL version string: 4.2.11995 Compatibility Profile Context
Within Catalyst Control Center / Info / under "Branch Software":
Driver package: 9.01.8-121202a-150296E-ATI
2d-driver: 9.1.11
Catalyst: 2.18
Well, it works on two screens (expanded desktop) and much better than without the ati driver. Also I notice -besides the "AMD Testing use only" watermark- that VLC has some not to nice, but still ignoreable issues with the icons at the bottom. Video therefore runs smooth and after switching VLC into fullscreen the pic is fine. Much better than before (ATI driver).

I have to admit that I before experimented with the ATI solutions discussed at ubuntuextreme. That didn't work for my ubuntu, but I didn't get rid of all the modifications it did to my system, like geting different kind of kernel updates (generic, I think). Works for me, but the config is no more out-of-the-box.

Looking forward to remove the watermark, Gnome (right now I run on unity) and work with Windows in the VirtualBox.