I’m not sure that is what he’s saying Mike. I think he’s just asking if he installs wpmu will all users have access to all subdomains. The answer is yes. Any user registered will have limited access as a ‘subscriber’ to all subdomains you create through wpmu.
You don’t need multiple installs to get multiple subdomains. Your root install, blog id 1, is the ‘main site’. All other blogs/sites are subdomains in wpmu.
