WebDAV that works:

WebDAV is a modern protocol to maintain web content. It is better than FTP in many ways. We support a Class 2 WebDAV server for all customers. It works perfectly for customers who do not run Windows operating systems.

The URL is http://webdav.m13.net/yourdomain.tld/

It uses the same name and password that you requested for FTP access.

WebDAV that doesn't work:

Microsoft has changed the way they support WebDAV with every version of their Operating System and every service pack. It's rumored that Microsoft might have gotten it right in Windows 7. Time will tell.  Customers who maintain web content and who use Windows are welcome to try WebDAV, but I gave up on it.