I've setup a Turnkey RCS server, and installed LikeWise-Open to allow Active Directory users to authenticate to the machine.
I've created an AD user group to contain the users which will have write access to the SVN repositories, and I've changed the permissions of the repositories folders so that the group has rwx permissions.
Group members can checkout the code, but are unable to checkin:
svn: E170001: Authorization failed
Any ideas would be appreciated :)