here is my output, I am running debian sid using some svn packages.
I have the nvidia driver installed and working with my 5200.
I am using dual monitors. And I get the same thing regaurdless of whether or not kwin is working.
wired@wire:~$ beryl --replace
**************************************************************
* Beryl system compatibility check *
**************************************************************
Detected xserver : NVIDIA
Checking Display :0.0 ...
Checking for XComposite extension : passed (v0.3)
Checking for XDamage extension : passed
Checking for RandR extension : passed
Checking for XSync extension : passed
Checking Screen 0 ...
Checking for GLX_SGIX_fbconfig : passed
Checking for GLX_EXT_texture_from_pixmap : failed
No GLX_EXT_texture_from_pixmap
beryl: Another window manager is already running on screen: 0
beryl: No manageable screens found on display :0.0