ajw,
I'm assuming that you restarted apache after changing the vhost file and the apache2.conf file.
You can look at this link which offers two options:
http://stackoverflow.com/questions/7516 ... web-serverYou can make the changes in the link above (probably just one or the other) in your vhost file or an .htaccess file in the site's root directory. Using .htaccess doesn't require a restart to apache, though you'll need AllowOverride All in your vhost file for .htaccess to override setting in your vhost.
MSJ