Enabling clean urls (really, fixing a broken configuration of Apache to allow path rewriting). Changes/additions in bold.

(Note: this example is for overall or default redirection, but the relevant parts in bold apply to any Drupal Apache conf file.)

NameVirtualHost *:80
<VirtualHost *:80>
    ServerAdmin webmaster@pwgd.org

    DocumentRoot /var/www/drupal-5-live
    <Directory />
        Options FollowSymLinks
        AllowOverride All
        Order allow,deny
        allow from all
    </Directory>
    <Directory /var/www/drupal-5-live>
        Options Indexes FollowSymLinks
        AllowOverride All
        Order allow,deny
        allow from all
    </Directory>

</VirtualHost>

http://drupal.org/node/43783#comment-93511