This book is intended primarily as a reference and learning tool for experienced developers who need to master ADO.NET. You don't need experience with ADO, but you should be familiar with .NET basics such as assemblies, events, metadata, and the Common Language Runtime. If you are new to .NET, you'll be well served by starting with an introductory work such as .NET Framework Essentials by Thuan L.Thai and Hoang Lam (O'Reilly and Associates, Inc.).
This book also assumes you know the basics of developing database applications. The examples in this book use the Northwind sample database, which is automatically installed with SQL Server and available with the freely installable, scaled-down version, Microsoft Data Engine (MSDE). If you use a different database product, you won't be able to run all the examples as written, although all the concepts will still apply.
Finally, to get the most out of this book, it's strongly recommended that you know the SQL language. If you're new to SQL, you should supplement this book with such books as SQL in a Nutshell by Kevin Kline and Daniel Kline (O'Reilly). You may also want to read books that target the specific SQL extensions used by your database product, such as Oracle PL/SQL Programming by Steven Feuerstein and Bill Pribyl and Transact-SQL Programming by Kevin Kline, Lee Gould, and Andrew Zanevsky (both O'Reilly books).