Multisite set up (one domain)

I already have an installation of Drupal that I have been using for our redesign. We need a series of "community" sites for specific communities in our organization, so I was going to set up separate sites for each one, so they are able to change the design, administer it, etc. (although I would like to use the same user table as the main site and just grant permissions per community site, it's not a deal-breaker)

However, I find all of the multisite instructions convoluted and confusing. Most are for sites across multiple domains, where I simply need multiple sites for the same domain.

For example:
dept.missouri.edu <--main drupal site
dept.missouri.edu/community1 <--community site
dept.missouri.edu/community2 <--community site
...

I have those folders set up in, for example:

• [drupal folder]/
  • sites/
    • community1/
      • files/
      • modules/
      • themes/
      • settings.php

What do I need to do to set up and get the community sites to point to the urls above?

Thanks

Drupal 6.14 + LAMP (MySQL 4/PHP 5/Apache 2)