Have you considered Google Calendar? It allows you to export your data in xml and several other formats so that you can sync the data. The info would be accessible via internet, has most of the top features such as reminders by SMS, email and popup notice on your computer. Go to google.com, if you have a gmail acct loginhttp://www.google.com/calendar
here is a sample calendar that I created for a friend http://harmonywellness.org/classes-yoga-wellness.html
. It only took me 30 minutes to add the items to the calendar. On the example calendar page you can see the options available to download or insert. Also as far as being accessible on the internet you can keep all or some of the data private.
It has been a life saver for me for appointments due to the reminders going to my phone by sms. Email to my desktop and the popup on my laptop.... although I have no excuses on why I am late now!!
Good luck. Let me know if you have any questions or if I can help.
have a great weekend,