Cheapest solution for central outlook address book?

We have a few workstation linked to a central windows XP system for file storage and internet sharing. All of us use outlook and it would be great if there was a central area for our address book and maybe calendar.

What do you think is the cheapest (maybe free) solution?

Thank you

 

I dunno how well this works but here is a free solution:
Sharing your Outlook information

 

Thanks, it seems that this service is no longer avalible

 

There was recently a round-up in eWeek of all the Outlook-compatible alternatives to Microsoft Exchange. These reviews should help you plenty:
http://www.eweek.com/article2/0,1895,1846659,00.asp