Drupal 6 generally is a solid version, notwithstanding the INSTALL.txt issue. It has good RDF support as well, including the ability to add and manipulate arbitrary triples using the RDF module. The Relations API module provides an easy user interface to add SeeAlso relations to nodes, but not to include nodes in arbitrary triples.
From the README.txt that comes with the Relations API: ” Currently supports bidirectional node relationships based on the rdfs:seeAlso predicate. This could in the future fairly easily be extended to include support for user-defined predicates and for unidirectional relationships.” – so this was part of the possible future plans, at least.
Since most of the RDF work appears now to be focusing on Drupal 7, I’m hoping that arbitrary relations make it in there. What I would really like to see is the use of the taxonomy terms vocabulary that the RDF module auto-generates used as the predicate set – that would essentially reach the “en:anyword” goal mentioned below, and in a widely used CMS! Perhaps this will be possible by extending the Relations API. For now, using it in standard form at a teaching tips site, http://bteaching.com