I've looked at the numerous threads on using subdomains with a single Drupal (CVS - 4.6.0) install.
I've installed that version, but am unable to figure out yet if I can do the same with just subfolders:
Single install at: site.com/drupal
Need to create full drupal sites for users (but ok if a single admin handles all administration).
User1: site.com/drupal/user1
User2: site.com/drupal/user2
User3: site.com/drupal/user3
And each user site can be customized, as to which user can do what at each site (add, edit, update, etc).