Hi all,
a little background info before i jump into the problem.
I'm working on a multi-site, using drupal 5.3 but upgrading to drupal 6 upon the official release and module updates. The site is a newspaper/media collection of websites. it's not that important what the sites are about since it can be about anything. so on one site it will be a pro journalistic content, another site or subdomain with user generated content, another site for videos like youtube, and another for music and photos. each site operates on it's own and has its own managers and content providers.
to make a long story short, we have all these sites, but we are planning on making another site that is entirely about the user, so in order to view the content on all the other sites you can have register on this site, we want the database kept separate of the content and other site related info... this database only has the user info... we're building a lot of other tables and fields on the user db along with several modules that would harness the power of these new tables and feed them into the other sites (this module along with several others in the works will be released as contributed modules)