Calendar Hack Req - 'Invite Only' Events

[kall]

I don't know if this has been done already, but what I am looking for is the following:

Member creates Private Event using calendar.

Member then chooses other members to invite to this event by clicking a link somewhere (in their profile, in the popout box when you click on their online/offline button in a thread...somewhere).

The person they have chosen to invite receives a PM advising '*membername* has invited you to their Private event, click here to view the event'.

They click on the link and then are able to view the event details.

They then choose whether or not to add themself to the 'Attending' list (I believe a similar hack is available for this 'listing' function.)

If a member has not been 'invited' by the event creator, they cannot see the event at all.

The member who created the event can see a list of attendees, along with those members yet to RSVP.

Is this do-able? Or even better, already out there somewhere?