Vista Calendar problems

A serious problem I am having with Vista calendar is that it is frequently
not alerting me to appointments/events. Sometimes days will go by and
abruptly I'm presented with a list of past due items. There may be a "good"
reason for
this happening but I can't imagine what it is as I log into the account
associated with the calendar at least once a day.

Also, is there any way to truly share a calendar between users on the same
machine? I've used the sharing options but always end up with copies of the
calendar and they don't update themselves when anyone makes a change.