Sharing outlook 2007 pst files

Is there a way to share all aspects of outlook 2007 between 3 desktops and one laptop. I have a client that is saying that is what they did in the past. The only thing I can think of is to leave a copy on the server. However they are insisting that they could share contacts as well. With that being said I thought about sharing the folder on a mapped drive, but thinking about that it may cause writing issues. Any suggestions would be great. One last thing this is a residential client.

Thanks
Adam

No, you can't 'share the pst' directly -- think about it -- (3) users saving appointments?

You can update the calendars of other users with the proper settings.
I'm not sure, but this may require a Domain Controller environment and not just a
Workgroup (ie simple Lan) setup.

That is what I thought and that is what I have reading. However, my client is saying that were able to do that and I cannot get it to them.......
Do you have any suggestions on any 3rd party applications. Or, I set it up leaving a message on the server for 10 days.
Any help or suggestions would be great. I know this is a weird suggestion, but this is the state I am with these people.

Thanks
Adam