[support] intranet/extranet combo - good idea?

Hi, I'll be developing both an intranet and an extranet for a client (a church). Now, I'm thinking of doing this with subdomains and a common codebase, like: www.churchname.com intranet.churchpage.com This would enable single logins for the staff, but I'm curious if this the way to go as I haven't really found a lot of info about these kinds of setups on drupal.org. is this a good way to do it, or do you think I will run into too many problems regarding security and other stuff? Is it better to separate the intra- and extranets? thanks! Morten