Update as of 10/2/2014:
For users using our drive mapping service on Windows, we now strongly recommend installing our WebDAV Drive Mapping Tool:
It is extremely easy. Just log on to the tool and you will be able to map a drive. You don't need to optimize the performance yourself any more. The tool will automatically fine tune the performance and reliability for you. As the result, DriveHQ Enterprise WebDAV Solution is more reliable than almost any other WebDAV services.
For system administrators, you can configure your sub-users to automatically map to a specific folder. It works just like your in-house file server, you can map multiple drives, incl. shared drives and set various levels of permissions to different users.
More specifically about your question "map a user's home drive from within Server 2003 to the Webdav drive", I am not sure about it. You might be able to do so, but I don't feel this is a good way. Instead, you can install our WebDAV Drive Mapping Tool. As the group administrator, you can configure all sub-users to map to a folder automatically. They can map multiple drives to different folders. This might solve your needs.