Multi User Calendar with Outlook and iCal integration

Hello I need the following

1) A Multi User Calendar, where the calendar can be viewed by anyone but cannot be updated unless they are logged in.

2) The ability to update the calendar with events/appointments.

3) Outlook and iCal integration, so that when a user updates this calendar it also updates their outlook/ical calendar.

So when a user logs in they have the option to add their exchange or ical address and for it to be sync both ways.

So Calender Outlook / iCal.


I hope this makes sense

The price is fixed as I can buy this script for a bit more than £100 but prefer to give work to a programmer who needs the money than a company who makes loads already.