IIS pass through authentication with UNC paths

We have continual trouble with setting up an IIS 6.0 virtual directory to do windows authentication in a load balanced environment. We believe that the problem consists of a double hop authentication for the iis anonymous user and the connect as user for the virtual directory witch is mapped to a UNC path on another server. We eventually got this to work but did not have a solid answer as to what made it work. We believe it has to do with setting up an SPN for that servername and username that the connect as user is using. I am working on a more detailed writeup for this and will post it soon. After a month and we are still seeing issues with pass through authentication. If anyone out there has any ideas, I am open to them.