Almost all popular calendar programs can handle the iCalendar (*.ics) format in one way or another.
The basic structure of such file is as follows:
Code:
BEGIN:VCALENDAR
VERSION:2.0
METHOD:PUBLISH
BEGIN:VEVENT
UID:
DTSTAMP:20060310T000701
DTSTART:20060216T091500
DTEND:20060216T111500
SUMMARY:summary or subject
LOCATION:location
DESCRIPTION:description text
END:VEVENT
BEGIN:VEVENT
UID:
DTSTAMP:20060310T000701
DTSTART:20060216T124500
DTEND:20060216T141500
SUMMARY:summary or subject
LOCATION:location
DESCRIPTION:description
END:VEVENT
END:VCALENDAR
Just copy this into a text editor and save it as a *.ics file.
more info:
link or if you're really hardcore:
link 
By default outlook can only export one appointment at a time. To export multiple appointments take a look at
this script