I'm looking for a scheduling program that can be shared

I've been looking for a software program I can use to schedule appointments, but it has to be something I can use on my computer as well as one other computer. I need the program to be accessible for both computers at the same time. If I update something it needs to be shown on the other computer and vice versa. The operating system on the first computer is Vista and the other is XP. I would really appreciate any suggestions.
 
There's a Google Docs / Calendar that's stored online, but that's not the same as collaboration in realtime.

try google collaboration tools
 
PIM Xtreme is interesting:

Requirements are

  • The requirements for running PIM Xtreme™ are:

    * Microsoft .Net Framework 2.0
    Required on client machines (those on where PIM Xtreme™ will be installed).

    All other stuff that PIM Xtreme™ requires is included in the packages. That is:

    * MySQL Connector/ODBC 5.1 (before PIM Xtreme 0.8.0 the MySQL Connector/ODBC 3.51 is required)
    * Microsoft ReportViewer

    You will also need MySQL Server, which is included on the "all-in-one" package (the big one) but NOT on the simple package. There are no hardware specific requirements for PIM Xtreme™. Refer to Microsoft .Net Framework or MySQL requirements for more details.
This is all GNU Public License (aka free for non-commercial use) software,
but the MySQL install can be a challenge for some.
 
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