Sven Berg schrieb:

How do I export a calendar from Outlook 2007 into an ics-file? Thanks,
Sven

Found it myself:

Outlook 2007 - Go - Calendar.
If you have more than one calendar, click in the reading pane on the
one you want to export.
go to: File - Save as - Options - Date range. Choose "whole calendar".
Press OK - Press Save.