I am using OSX Leopard and would like to sync iCal with some other system so at home, on a Linux box, I can see the calendars. I thought about Google calendar, is it possible?
To simply copy the information there, you can export your iCal calendars as .ics files, and then import them to Google Calendar with the web interface.
CalDAV syncing is possible without additional software, but can end up looking quite ugly if you have multiple calendars (Each calendar will display under a different account header or subfolder).
If you want Google-based calendars to appear in a normal list (just like MobileMe calendars would look) you do need additional software. I personally use BusyMac software's product BusySync... it's a preference pane that allows you to sync iCal's backend with Google, completely seamlessly. Spanning Sync 3 is another option.