How would YOU implement cross-platform calendaring / email / contact management?

[Sesshi]

If you were to start from a blank sheet of paper and were to implement a networked, remotely accessible PIM environment for several people who were using Macs and PC's, how would you go about it?

I have the opportunity to go 'blank slate' with my infrastructure and a startup's.

I'll just ask the simple single question for now, and flesh it out as the thread progresses.

 

[MacsRgr8]

Wait for Leopard Server

edit:
If you want to use an Xserve, Mac OS X, for the back-office, and keep it "non-Micro$$oft" you could think of using Kerio Mailserver.