You'll need to know some AS3 before you start using this book. Sure, it's a "Beginner's Guide", but beginner refers to your knowledge of Facebook development, not Flash development!
All of the code in this book is written using classes inside AS files; there's no timeline code at all. You don't have to be an OOP guru to follow it, but you must be familiar with class-based coding. If you aren't, check out these two resources:
AS3 101 A series of tutorials to walk you through the basics of AS3 development. In particular, read from Part 8 onwards, as these deal with OOP in AS3: http://active.tutsplus.com/series/as3-101/.
You should also know how to create and compile a SWF project, and be familiar enough with HTML to be able to embed a SWF in it. We'll use SWFObject for this purpose (this is the default embed method used by Flash CS5); if you're not sure what this means, familiarize yourself here: http://code.google.com/p/swfobject/.
All important AS3 classes and keywords used in this book will be briefly explained as they become relevant, so don't worry if you haven't memorized the LiveDocs yet. Speaking of LiveDocs, remember that you can always use them to look up unfamiliar code: http://help.adobe.com/en_US/FlashPlatform/reference/actionscript/3/index.html.