Syncing iCloud’s Calendars on Snow Leopard is quite simple. The only information that requirement is your iCloud Server Number which nearly always in the form pXX-caldav.icloud.com.
To find this number open Safari and login to your iCloud account.
Click on Calendar and then chose Windows —> Activity from menu bar.
In the window you should see something that is similar to this:
The iCloud Server Number is the first part of the address namely p01 in this case.
Open iCal’s Preferences, then pick the Accounts Tab. Click the plus sign at the bottom left.
Fill in the fields with the following settings:
pXX is your iCloud Server Number from above.
Now click create create. If it asks you to pick a server choose
pXX-caldav.icloud.com from the above settings.
It should work now!