I think I have everything solved. I think that the kernel image was updated so that the nvidia module was not the correct version. I HAD built another module (following the excellent instructions on this site: http://home.comcast.net/~andrex/Debian-nVidia/installation.html), but somewhere something must have gone awry. I started all over again, and rebuilt a nvidia-kernel-*.deb and then installed it. That went off without a hitch. After that, nvidia-glx DID get installed from apt-get.
So I think the original problem was that xorg had been only partly upgraded (since I wasn't using official sources), then after xorg was properly upgraded I had done somethign wrong in the building or install of the nvidia modules causing nvidia-glx to fail. Thanks for everyone's help. Craig
