"Unable to create dir" error during installation.

Trying to get my first installation of Gallery working. I'm using the .deb packages from Debian.

What seems to be the last screen of the setup program, after Step 4 shows me the configuration file, when I click on "Save Config," I get a page that just shows in red "Unable to create dir:" (there's nothing following the "dir:")

The directory where the .htaccess and config.php are written seems fine; the files are written there properly. The /tmp and <web_root_directory> directories are write-able by everyone. The <web_root_directory>/albums directory was created and is owned by the user which runs Apache.

When I searched the FAQ and forums for '"Unable to create dir"' I noticed that most of the entries showed the name of a directory after the error message. None of the other posts seemed to address my problem.

I haven't gotten past the setup, so I haven't seen a Configuration Wizard, but here's the information on versions:
Gallery 1.2.5 (from the changelog file)
Apache 1.3.26
PHP v4.1.2 (from the Gallary Setup: Step 1 screen)
Debian GNU 3.0 (woody)

Thanks for your thoughts and suggestions on how I can understand and resolve this problem.

-Kevin Zembower