Outlook Calendar and netfolders

I have a client that for security reasons don’t want to have their LAN connected to the Internet.
They are only eight people working in the office and they have other mashines connected to the Internet. They think this is a solution that works OK for them.

The problem is that they would like to use Outlook calendar as their schedule, this means also that everyone must be able to write to each others calendars. They also need to sync their own calendar with 3com Palm computers.
I now wonderif this is possible with Netfolders only installed, or do I have to set up e-mail server as well?
As you can see there is also a grate differense in cost for my client here.