The Zalman ZM-GWB3 is compatible with most of modern graphics card models. Just take a look at the following scheme and table:
So, the water-block cannot be installed on the GeForce 7950 GX2 due to obvious reasons and will be useless on GeForce 8800 series cards due to its too small base area.
I installed it on a GeForce 7600 GT for my tests. To do that, I first put rubber circles on the fastening barrels and inserted them into the holes in the graphics card PCB.
The barrels are fastened at the reverse side of the PCB with spring-loaded thumb nuts through plastic spacers:
Then you just fasten the water-block with screws to the installed barrels.
You can refer to the official manual in PDF format for details.