403 Forbidden errors after completing 5.18 install script; unable to create first user

Hi-

After successfully running the web-based installer, I am now getting '403 Forbidden' errors. I created the DB, entered the connect information into the install pages, and Drupal created the DB tables, finishing with the page that says 'Welcome to your new Drupal website! Please follow these steps to set up and start using your website:'

But then when I click on the link in step one ('create your first account'), I get a '403 Forbidden' error. The URL that errors out is 'http://d5staging.www.sitename.com/?q=user/register'

I have the drupal install defined in my httpd.conf as a virtual server 'd5staging.www.sitename.com' with 'path/to/drupal' set as the DocumentRoot for the server.

If I type 'http://d5staging.www.sitename.com' into my browser I get a '403 Forbidden' error, but if I type 'http://d5staging.www.sitename.com/index.php' in then I am taken to the 'Welcome' page.

Several other non-Drupal virtual servers on this same apache are running fine. Also, the Drupal installer did not produce this error while it was running.

I've searched on drupal.org and also on several search engines and it seems like this is a common problem, with several suggested fixes, but no definitive answer.

Things I've tried (which haven't resolved the problem)

*commenting out the Options Indexes and Options Followsymlinks in the drupal .htaccess file
*chowning all the drupal files to have the same owner as the webserver
*adding in the RewriteBase directive in the drupal .htaccess as described in the .htaccess file comments
*adding directives to the Virtualhost in the httpd.conf to enable Options Indexes and Options FollowSymLinks for drupal virtual server

Can anyone shed some light on the fix for this?

What would be especially helpful is an explanation of what the htaccess file is doing - it has a lot of regular expressions in it and it seems like it could be the source of the problem.

Thanks!