You should have a fundamental understanding of Windows server operating systems to use this book. If you have experience installing and running Windows Server 2003 and Windows XP, you will get a lot out of this book.
To an extent, I assume you're running Windows Server 2003 in a business of some significant size. Many of the examples in the book assume a network infrastructure that is most often seen in mid- to large-size businesses, such as a distributed Active Directory forest. However, I do attempt to frame each example with the assumptions I make for it. In most cases, these examples will scale up or down to fit your specific environment.
You do not need an in-depth understanding of security topics or a Ph.D. in mathematics to read this book. Who would use a book like that anyway? Those people already know everything.