I am currently writing another solution to this and will post it here in a while but this is a great introduction to one of the more trickier IIS concepts i have been forced to handle.
http://blogs.msdn.com/nunos/archive/2004/03/12/88468.aspx
and here is some more to read on the subject http://drowningintechnicaldebt.com/blogs/shawnweisfeld/archive/2006/12/06/The-_1C20_Double-Hop_1D20_-Issue.aspx