Multi-Domain Creation with single starting point window

Chris Spencer
I would like to create a multiple sites or domain in which three types of courses with their own ownership, branding and pedagogical models each have their own separate area, but still available and searchable from the same starting point. Within each area they will have their own course categorisations. They must be able to support reference links to complimentary courses in one of the other domains. Can this be done in Drupal? If so how? I.e. With which app modules is it best done? (e.g. Drupal Multisite/ Virtual Sites? Categories ?)