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