This book is definitely for Advanced VB developers. Accessing the API is something that you do not do all the time as a VB developer. It will tell you though almost everything you need to know how to access the Windows API from VB, IF you have the heart for it.
If you don't have it, probably Appleman's other book, "Developing COM/ActiveX Components from Visual Basic 6" is for you. Not only is it easier to understand and truly worthwhile, but you'll be easily proficient in designing classes, objects, DLLs, Exes, Controls, etc., extremely useful concepts I never thought I'll understand before I started reading it. Now, those, I can say, can even be for the faint-hearted.