I've been struggling with trying to find .Net 2.0 version of NDoc for quite a while now. So long as you aren't using generics in your code, you can generate documentation for 2.0 using the old NDoc if you modify some config files. You can find out how to do that by going through some of the discussion threads on the sourceforge page for NDoc.
NDoc is pretty sweet, though I'd be interested to see other free/open tools that are out there.