I can't say enough good things about this book. But let me try.
If you want to understand how 98/NT/Win2K works under the covers, read this book. Brain and Reeves 'break it down' for you in simple language and C code that works.
If you hate Windows and think Unix is the only true OS, read this book. You'll still like Unix better, but you'll appreciate how truly wonderful Win32 is.
If you need to write code for the Win32 platform, especially server code, read this book. I bought this book when I needed to learn how to write NT services. An hour later I had my first service running.
I also learned how to write threaded code using this book.
Don't wait another moment. Buy this book now. You'll keep it at your side and use it all the time.
This is a classic work on par with Stevens' TCP/IP books.
I only wish Brain wrote a book for every subject that I needed to learn. Oh, wait, he has...