Hi,
I gave the following reply to someone recently, but I don't know how they got on:
It should be possible to do this using MAPI objects, how confident are you writing code? I've done some work linking to a public contacts folder, so I should be able to give you some help, but as I don't have a public calendar or permissions to set one up I can't give you any complete solutions.
You're probably best starting by looking through the Microsoft Knowledge Base for MAPI. I'd suggest you then try & write the code to use the default calendar first, just because it's a little easier, then, once that's working, change it to look at your public calendar.
Sharon