Multisite for intranet/extranet
Multi-site is designed for a shared codebase with seperated content.
It is possible to share a few tables within all multi-sites without complications (e.g. users, roles, session) but espacially sharing  of content and content-types is not quite easy.

I would suggest Domain Access: http://drupal.org/project/domain


  The Domain Access project is a suite of modules that provide tools for running a group of affiliated sites from one Drupal installation and a single shared database. The module allows you to share users, content, and configurations across a group of sites