Check out Jake's articles on the matter..
http://www.codestore.net/store.nsf/unid/EPSD-587VVX?OpenDocument
This will help with the actual mailing of HTML, not sure about hiding a link.
Or try this Google search:
http://www.google.com/search?sourceid=navclient&ie=UTF-8&oe=UTF-8&q=Domino+HTML+mail
Good luck!