I see now how I could have used IWeb for this... I had thought all the methods required the IWeb Authentication header but in another example I came across of yours, I saw that wasn't always the case.  At any rate, I ended up not using IWeb but borrowing from some of the methodology therein to implement the security for accessing the webservices.  Great stuff!  This project is turning out nicely... a lot more responsive and "cool" than using UpdatePanels.

Thanks again.