iCal losing calendars

[Jim Shimozawa]

Hello iBook people:
Yesterday, unexpectedly iCal (1.5.1) quit.
I was not doing anything special - like adding software, running 
Norton, etc.
Prompted with a screen asking me, I submitted a bug report to Apple.
When I restarted iCal, all of my calendars were gone.

Today one came back, but I'm missing others.
How can I retrieve my lost calendars?
I have old copies of my calendars on iDisk that I backed up using 
Backup a few weeks ago, but they are dated .
Thank you all in advance.
Jim

iBook 700/640/CD/20 - running OS 10.3 (Panther)