In addition to the extremely fine book you're currently reading, there are only two other API-related books that we would recommend:
Dan Appleman's Visual Basic Programmer's Guide to the Win32 API, ISBN 0-672-31590-4, published by SAMS.
Steven Roman's Win32 API Programming with Visual Basic, ISBN 1-56592-631-5, published by O'Reilly.
3.142.114.245