I've done some looking around at automated documentation programs. There's HeaderDoc, which Hans-Christoph mentioned, AutoDoc, Doc++ and Doxygen. Of all of those I would go toward Doxygen, as it runs on Linux, Windows, and OSX and is GNU GPL, while HeaderDoc is APSL. Doxygen is used by KDevelop and Mozilla for their source documentation.
I haven't seen anything that gives wiki ability out of the box, but it should be easy to add some sort of wiki comment system by means of links. The auto-generated docs act as a skeleton that is fleshed out with a wiki. I don't have a wiki server at my disposal, so I can't give an example of it, but Doxygen is very configurable and allows custom footers that could include links to a wiki via some sort of server side scripting.
I've written a brief Doxygen config file and created documentation out of the 0.38 CVS HEAD src directory so you can get an idea of Doxygen. I did not alter the source files at all, so the commenting is *very* sparse. The Test: http://www.0x09.com/temp/doxydoc/html
The only actual work I did to get the test: http://www.0x09.com/temp/doxydoc/
Doxygen help documentation http://www.0x09.com/temp/html
=== likage: === HeaderDoc http://developer.apple.com/darwin/projects/headerdoc/
Doc++ http://docpp.sourceforge.net/
Doxygen http://www.doxygen.org/
AutoDoc http://www.oche.de/~akupries/soft/autodoc/
Let me know all y'all's thoughts on it, and I'll see what I can set up so we can slowly start improving the documentation.
Cheers, Ian