First, you will want to protect the folder you will be accessing using DAV with some sort of Access Control. Do this in the Admin Server by selecting the Folder Contents button of the VirtualHost you wish to add WebDAV support to. Set up a realm based or IP based restriction for the folder.
Next you will need to add some configuration to the httpd.conf file using a text editor such as vi or BBEdit. Add the line:
DAV On
To the container at the bottom of the httpd.conf file which configures the realm you just added.
Finally, Add the line:
DavLockDB /etc/httpd/DavLock
to the very end of the file.
Restart apache using the iTools application or the Admin Server and you should be all set.
If you only want DAV functions to be protected by the realm (all other users can access using a web browser), enclose the "Require" directive in a Limit container like in this example:
<Directory /Library/WebServer/WebSites/www.tenon.com>
DAV On
<Limit PUT POST DELETE PROPFIND PROPPATCH MKCOL COPY MOVE LOCK UNLOCK>
Require user dav-user
</Limit>
</Directory>
Make sure that the Limit container is all one line. This will limit WebDAV functions to the iTools user "dav-user". | 
