Hi Seth, I recommend Nick's book:
The Apache Modules Book: Application Development with Apache ISBN-10: 0132409674 ISBN-13: 978-0132409674I bought the book, after I had already written my authentication module, as a reference. It explains the memory structures you were talking about and actually everything you need to know for writing your own modules.
I guess I would have saved a lot of time, if it had been available earlier. Helmut