This hint is for Tiger only -- you'll have to modify it on Leopard or Snow Leopard, because of changes to iCal's folder structure.
I've recently switched to Mozilla Sunbird because it looks a lot nicer and runs faster than iCal, although it can't directly use iSync, so I can't synchronize the calendars on my laptop with my phone. By looking around in iCal's folder, I found out that you can copy a calendar file (.ics) from Sunbird into iCal and use that to synchronize with iSync. You can then load that synchronized calendar back into Sunbird.
There's a lot of mucking about, but it's well worth it :).
0#!/bin/bash # Copies Sunbird calendars (Work.ics and Personal.ics) to iCal for iSync with phone # Syncs everything with phone, then copy back to Sunbird # Make sure Sunbird is restarted! # Backup existing calendars cp /Users/joe/Documents/Work.ics /Users/joe/Documents/Work.ics.bak # Copy Sunbird calendar to iCal, ready for syncing cp /Users/joe/Documents/Work.ics "/Users/joe/Library/Application Support/iCal/Sources/614ED0EF-9429-4241-B8F7-26DA48E737EA.calendar/corestorage.ics" # Syncs calendar with phone /usr/bin/osascript /Users/joe/bin/autosync.scpt # Runs iCal for a second to set sync /usr/bin/osascript /Users/joe/bin/ical_start_stop.scpt # Copies back synced iCal calendar for Sunbird usage cp "/Users/joe/Library/Application Support/iCal/Sources/614ED0EF-9429-4241-B8F7-26DA48E737EA.calendar/corestorage.ics" /Users/joe/Documents/Work.ics
tell application "iCal" to activate tell application "iCal" to quitThe above script also references autosync.scpt, which is a script taken from this hint, which I copied and saved in Script Editor in the bin folder in my user's home folder.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20091109002714207