It will be very useful for development of custom modules if DotNetNuke API Reference would exist.
The core has XML comments and VS 2005 supports XML documentation in VB.
I didn't find any tools that currently fully support .Net 2.0.
NDoc is not fully implemented version for .Net 2.0, but has some workaround, which doesn't work for me.
The modified version 1.3.1 of NDoc started to build help but then got an NDoc.Core.DocumenterException
“Method may only be called on a Type for which Type.IsGenericParameter is true.“
I didn't try yet http://www.kyrsoft.com/opentools/qdocviewer.html.
I was able to run utility from http://msdn.microsoft.com/msdnmag/issues/02/06/XMLC/ to show XML documentation for individual classes as HTML pages,
but it doesn't have search capabilities that Help(MSDN) format has.
UPDATE: Online help(for 3.2.2) is now available here. I've posted some more ideas about it here.