Volunteer Scheduling

Hello. We're already using Drupal 6.x for our organization's site, along with CiviCRM 2.1 (mostly for CiviEvent, for event registration). We're running our calendar still through Google calendar, and linking to the event registration pages from there). We're not sure how well any online calendar/sign-up system would work for our volunteers, and, as I'm pretty new to Drupal, I don't want to sink more time than is necessary into getting something set up.

We need an easy way for our teen volunteers to register/sign up for volunteer times. Some of these would be recurring (we have regular teen volunteers on Saturdays, as well as more sporadic times for teen volunteers - either during the summer, or special events, etc.).

I need the following if possible:
Recurring sign ups (so a teen could sign up for 10-1 the first Saturday of every month, for instance)
Limits (i.e., no more than two in the 10-1 slot, no more than 6 for x special event, etc.)
Private/log-in required
Possibly blocking volunteers from seeing who is signed up for other slots, just whether they're available or not.
Ability to block users from changing their sign-up without admin (volunteer coordinator) approval

Would it be relatively easy to set this up with Drupal, and if so, what would be best to use? (Organic groups? Event? CiviEvent? Something else?)

Thanks!