Sync iCal between OSX 10.4.11 and OSX 10.5.8

In what ways can iCal be synced between OSX 10.4.11 and OSX 10.5.8?

Can iCal 2.0.5 be installed on OSX 10.5.8 so both OS run the same version of iCal?

If so, how?

Can iCal Calendars be moved to an external drive, and both iCal installs pointed to same location?

From OSX10.5.8, I've copied files in ~/Library/Calendars/
to a folder on the external drive, then pointing OSX10.5.8 ~/Library/Calendars/ to the external drive folder.
As far as I can tell, iCal works fine, and I've deleted and edited calendars.

I then pointed OSX10.4.11 ~/Library/Calendars/ and OSX10.4.11 ~/Library/Application Support/iCal/Sources/ to the same calendar folder on the external drive.
Different calendars displayed in iCal 2.0.5 on OSX10.4.11 than on OSX10.5.8 and kept reappearing after deleting and restarting iCal 2.0.5.

I deleted 10.4.11 ~/Library/Calendars/ after finding reference indicating that iCal on OSX10.4.11 has different structure with data stored at ~/Library/Application Support/iCal/Sources/ instead of at ~/Library/Calendars/ on OSX10.5.8

(I must have mistakenly thought there was a ~/Library/Calendars/ folder in iCal 2.0.5 on OSX10.4.11)

I then deleted all the calendars from iCal 2.0.5 on OSX10.4.11 except one which would not allow deletion, and they remained deleted after shutting down and restarting iCal 2.0.5, but calendars stored on external drive still do not appear in iCal 2.0.5 on OSX10.4.11

Calendar .ics exports from iCal on 10.5.8 can be imported to iCal 2.0.5 on OSX10.4.11, but they do not retain structure.

Data from several calendars get mixed up together for some reason.

Any suggestions on how to get the two versions of iCal synced?
I have 2 drive partitions that I use and need to be able to share calendars between the OSX versions.