Actually i wasn't reading the original post carefully. I'm following the same wiki page (
CalDAV with Leopard iCal - Zimbra :: Wiki) and it doesn't seem to work over https. I get:
Unexpected secure name resolution error (code -9813)
It sounds like an Apple iCal problem that it doesn't work with self-signed certs, according to this link:
Apple - Support - Discussions - Getting error (Unexpected secure name ...