I followed the directions here.

This seems to work on Debian Lenny, but there is a world of unmet dependencies for Debian Etch.

apt-get update
apt-get install libopkele-dev

I also had to install a generic package not already installed on my system:

apt-get install automake

Then pull in the libdb dev package:

apt-get install libdb4.4++-dev

Then, download the source from http://butterfat.net/wiki/Projects/ModAuthOpenID/Releases.

Next run:

./configure
make
sudo make install