AJA Kona vs. Quartz Extreme

...and "some video cards". And by some I mean ATI's 8800GT among others.

From AJA's support site:

(Release Date 2/14/2008, TAR archive)
This 5.1 NDD version is recommended for OS X 10.5.2 users. Note: The AJA
KONA driver version 5.1 NDD is the same as driver version 5.1, but removes
the Macintosh Desktop Display feature.

With the regular version of the 5.1 driver, some users may experience issues with Quartz Extreme, the behavior of their computer displays, and in some cases, kernel panics may occur with certain graphics cards installed. If any of the issues mentioned occur, the driver version 5.1 NDD should be used instead of version 5.1. Driver version 5.1 NDD is also the recommended version for use with the latest Intel Xserve with Xeon 5400 series processors, model (MA882LL/A).