WMI, or Windows Management Instrumentation, is the standard method used by Windows to monitor and control services on network computers. 

Perhaps the first place to go to learn about WMI is the Wikipedia (http://en.wikipedia.org/wiki/Windows_Management_Instrumentation).  I'm been a bit active on Wikipedia since I was teaching at UNCC here in Charlotte.  Always make sure you look at the edit history (or simply glance at the edit history) to make sure you haven't wandered into a heated debate.  One reason I suggest that rather than our own resources is this:  suppose I were to make a pointer to the standard page out of the MSDN online documentation (http://msdn.microsoft.com/en-us/library/aa394582.aspx).  What happens to my link when MSDN is rearranged?  There certainly are links at the bottom of the wiki article to the standard references, but unlike my link, a team of people will update those links when they become stale. 

However, when it comes to books on the subject, my first place would be the Windows Internals book by Dr. R, one of our Microsoft technical fellows (with David Solomon)-- http://technet.microsoft.com/en-us/sysinternals/bb963901.aspx.  In about ten pages, he carefully defines the important terms and introduces you to the most important tools for browsing the repository and calling into WMI.  The 5th edition (covering Windows 2008 Server) is expected to be published in January of 2009. 

When I came to the DSC-Manage team, my predecessor left me two very good books.  Wes recommended the New Riders WMI: Windows Management Instrumentation book (by Lavy and Meggitt, (2002)).  Lavy has a MPhil from Cambridge, so I was right at home.  If you are a system administrator, then this is the book for you.  However, it doesn't go into the details of actually writing a provider, and I think it insufficiently warns the reader about the huge performance hit your programs take in doing ADSI tasks from WMI. 

The other volume I have is from Addison and Wesley, Developing WMI Solutions:  A Guide to Windows Management Instrumentation (2003).  That is the book that one needs to use if one is writing a provider (though really complex providers will involve looking at something like Robbins' book on writing device drivers).  Wes thought that this book spent a bit too much time dwelling on theoretical topics (there is a chapter about UML, for instance).

Next week, I want to talk about an actual problem I've run into working with a large customer -- the problem of token bloat -- and put it in the context of making decisions about the allocation of structures for an API.