Windows Update Internals

Hi,

Can anyone please tell me as to how can I get a detailed knowledge of how
Windows Update works? We are all seeing lots of Windows Update errors these
days. Sometimes the solution involves re-registering DLLs, sometimes
installing XML parser, etc.

I'm specifically looking at to know the following aspects in greater detail:

-> What are the different roles of numerous DLLs involved in Windows Update.
-> What is the role and involvement of XML parser.
-> There are now newer versions of BITS and WinHTTP. What are these for?
-> What is the role of “Impersonate a client after authentication� policy in
WU. If any PC does not show up this particular policy in User Rights
Assignments, is there a way to restore this policy?

Can anyone point me towards any appropriate resource that explains how all
these components work together for WU?

Thanks much in advance!
-Rajesh