How to add a new user to Subversion using DAV.
htpasswd2 -n USERNAME
This will give you the password. Add this to dav_svn.passwd. To find dav_svn.passwd chec /etc/apache2/mods-enabled/dav.conf there should be a setting there.
You'll need to add the user to the davsvn.authz file to set the groups. Check here http://davidwinter.me.uk/articles/2006/03/03/access-control-for-subversion-with-apache2-and-authz/ for instructions on setting up groups.