I am a bit late with this one, but here is a new version for NHibernate 1.2 GA. This also supports Castle Active Record, hopefully in a version neutral way.
You can get it here, or admire the UI here:
As an aside, I am thinking about adding Criteria Query functionality, since this is something that I use a lot. I am not sure yet what form this would take, at any rate it would involve runtime code generation, so that is complex (and sort of fun/pain).
I am opened to ideas.