What You Need to Use This Book
This book targets Visual Studio 2005 and the .NET Framework 3.0, which includes WPF (among other things). You'll also want the Visual Studio 2005 extensions that provide WPF templates that are mentioned in this book. You can download all of this for free[1] (even Visual Studio 2005, if you're willing to limit yourself to Visual C# 2005 Express Edition [2]).
WPF itself is supported on Windows XP, Windows Server 2003, and Windows Vista (and will be supported on future versions of Windows, of course).
[1] * You can find the links to download the .NET Framework 3.0 and the WPF extensions to Visual Studio at http://sellsbrothers.com/news/showtopic.aspx?ixtopic=2053 (http://tinysells.com/104).
[2] † You can download Visual C# Express from http://msdn.microsoft.com/vstudio/express/downloads/ (http://tinysells.com/105).