I had set up my 10.3 PowerBook as a WebDAV server so my wife, with the new 10.4 MacBook Pro, could see the calendars. This was working fine, but there were often complaints about not being able to update calendars from the "slave" machine.
So I created a calendar on the MacBook and published it to the WebDAV server. My problem came in trying to subscribe to that calendar from the 10.3 PowerBook. Subscribing to webcal://powerbook.local/ical/hers.ics was accepted, but resulted in a network error -132. I finally decided that this was caused by trying to access the WebDAV server on the same machine via the external network. Replacing the address with webcal://127.0.0.0/ical/hers.ics eliminated the error. So now we can both see her calendar, his calendar, and the house calendar.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20070305085654797