Great tip, thanks! Macintosh C Programming by Example suggested the shareware "Inside Mac Desk Accessory," but I'm not sure if that's available anymore; this seems like a good alternative.
I've also noticed that the original documentation for OS 8 and 9 is still available on the web—http://mirror.informatimago.com/next/developer.apple.com/doc.... Do you know if there was there ever a web-based version of the earlier Inside Macintosh?