No pkg-config file for xorg in Dapper?

[Dave M G]

Ubuntu Users,

I have been having trouble installing an Nvidia Geforce video card with 
Ubuntu Dapper Drake 6.04. I have been discussing the issue on the Nvidia 
Linux users forum here:
http://www.nvnews.net/vbulletin/showthread.php?p=862085#post862085

I'm turning here now because an Nvidia representative has suggested that 
as a next step I need advice from an Ubuntu group that could inform me 
about packages used by Ubuntu.

The reason is that he asked me to run the command:
pkg-config --variable=moduledir xorg-server
... and it returned no output.

When I told him this, he responded with this:

"Yes, the fact that the pkgconfig command produced no output is the 
reason why the driver isn't getting installed properly. That command 
should return the location of the xorg modules directory. Either Ubuntu 
has a bug such that its not shipping a pkg-config file for xorg, or 
you're missing the package that includes the pkg-config file for xorg. 
I'm more inclined to believe its the latter, since I'm not seeing a 
large number of Ubuntu users reporting this problem. I'm afraid I don't 
know which package Ubuntu uses that ships the pkg-config file for xorg, 
so you'll need to consult with an Ubuntu support group/forum for that 
information. Once you get that sorted out, reinstall the nvidia driver, 
and this problem should be resolved."

I looked in Synaptic and I have xserver-xorg package installed.

What might be the missing package I need?

Thank you for your help.

--
Dave M G