Hi Paul,
I've checked out a bunch of tools for this and the one that works best for me is PasDoc. It generates HTML and provides a build file (IIRC) for compiling the generated pages into a CHM. It can also do one or two funkier tricks like generating files for (IIRC) GraphVis, to generate a dependancy chart. These can get a bit messy for large projects.
It's comment format is simple enough and it does support a number of useful things like includes.
You can grab it from http://sourceforge.net/projects/pasdoc/
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