Recommendation for calendar and contact sharing from Outlook

Hello. I recently posted a request here asking about a sharewayre email
server and was pointed to Mercury. It works great. However, now the
company asked me for software to allow them to share their calendar in
Outlook.

The company is fairly small now and therefore has only Win XP
workstations (including their "server"). They are way too small for MS
Exchange. Currently they have two laptops and six desktops running XP
Pro.

DOes anyone have any recommendations of either shareware/open source or
reasonably priced commercial software? The ISP will be providing email
once the T1 is hooked up so they will not need any internal email
capability other than Outlook.

I did a Google search for calendar sharing software and was pretty
overwhelmed. I am considering 4Team and OfficeCalendar, among others.
Any suggestions would be appreciated.

Thanks.
Bill