Provided only one instance out Outlook is accessing it at any one time and
with the knowledge that it's unsupported and could lead to a damaged PST (so
make frequent backups), yes.  Googling the Outlook groups shows several
times in the past that your question has been answered.  Here's one from two
years ago:
<http://groups.google.com/group/microsoft.public.outlook.general/msg/b125a143faef3ad5>

There are several pretty good solutions. Start at this location

http://www.slipstick.com/outlook/share.htm

and take a look at the linked software and procedures.

Sharing calendar is very easy if all computers are running Outlook 2007.  If
that is the case, you can publish the calendar and invite others for view.
To do that right click on calendar folder and then publish.  Sharing other
folders is more difficult

Hy,

You can also try ShareO:
http://shareo.4team.biz/?pcode=610190201v4rqia

Mindoza.