Carsten, Piotr and Pete,

thanks for the replies so far - great to hear that it's possible to  
do plain ascii editing and still have the same data ready for syncing.

I tried to play with the ideas you mentioned, but I found out that I  
have no .ics-files in ~/Library/Calendars. I knew I had my iCal files  
stored there in the past (OS X 10.3.x). Currently I'm using OS X  
10.4.7 and it seems that some data is stored in

~/Library/Application Support/iCal/Sources

for each calendar in iCal, there seems to be a directory like:
E2A32ED1-CBD0-4A13-B397-3742B1680F17.calendar

which has 3 files in it:

corestorage.ics
Index
Info.plist

I was able to export my org-mode-data to an .ics file, but it seems  
that iCal imports data from that file and then creates a new file  
under the path given before (~/Library/Application Support/iCal/ 
Sources).

Question1: How can I force iCal to read and write to the .ics-file  
I've exported from org-mode?
Question2: Why isn't there a ~/Library/Calendars Folder?

Best regards from berlin

phil