nvidia-173 fails to install on natty

Using natty amd64:

# apt-get install nvidia-173
Reading package lists... Done
Building dependency tree
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies.
 nvidia-173 : Depends: xorg-video-abi-8.0 but it is not installable
              Depends: xserver-xorg-core (>= 2:1.8.99.905-1ubuntu3) but it is not going to be installed
E: Broken packages

# apt-get install xorg-video-abi-8.0
Reading package lists... Done
Building dependency tree
Reading state information... Done
Package xorg-video-abi-8.0 is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

E: Package 'xorg-video-abi-8.0' has no installation candidate