Doxygen
Doxygen is an automated method of documenting code... you add a few special comments to the header files and then run the Doxygen program, which spews out about 50MB of HTML files which document the code in a web browser.
You can download the software from:
http://www.stack.nl/~dimitri/doxygen/
You'll also need GraphViz from:
To generate the diagrams. And the Microsoft Help Workshop to build the help file from the HTML files:
There's a sample config file in the source directory 'Doxyfile': run the Doygen Wizard program, open the config file and press 'Start' to process the source. There's also another version which produces a cut-down file, 'MiniDoxyFile': that skips the diagrams and doesn't include the source in the files.