Collaborative Calendaring using Outlook client

>I was just wondering if anyone had any experience with some
open-source/FSF
>apps that can provide collaborative calendaring for Outlook Clients.
That's
>really the only functionality that my client would like that they don't
>currently have. I will be running a Linux based server in their office
to
>allow them to file share between Windows and Macs already in the office.
The
>transfer of most of the office to Linux will be slow at best.

I saw a few threads on the postfix-users list about this. No one seems to
have a silver bullet for Exchange calendaring. We can filter viruses, spam
and still do it faster than an Exchange box, but we can't give the masses
good calendaring. Please do post back if you find anything interesting and
even workable.

Tony Wasson