If your iCal is crashing and you have not updated to Leopard, I found an easy fix that stops the crashes in 10.4.11.
Just do this:
Go to library/applications support/syncServices; move that folder (LOCAL) to the desktop; restart. Move the syncServices folder from the desktop to the trash, and iCal stops crashing.
That's all you do. Then just empty your trash. Presto!