There is a way to add an iCloud Calendar in iCal in Snow Leopard.
Open iCal in Snow Leopard (if is up to date, it should be Version 4.0.4 (1395.7).
- Select 'Preferences' from the iCal Menu.
- Go to the Accounts tab.
- Click the + sign to add a new account.
- Select the 'CalDAV' option under the Account type.
- Enter your 'User name' which is your iCloud .me email address.
- Enter your iCloud 'Password'.
- Now comes the tricky part; the 'Server address'. See below.
It will be of the form pXX-caldav.icloud.com
(the XX would be numbers of the dedicated server). I was able to determine this value by sending an invite to another one of my other email accounts and clicking the 'Accept' button. This will open the reply in a web browser. If you look at the long URL, at the end there is a pXX value and that's the dedicated server.
Once that is done, the calendar will show up iCal. However, a few minor updates will need to be done so that it behaves just like in Lion's iCal.
Click the 'Server Settings' tab for your new calendar and update the 'Server address' with your pXX-caldav.icloud.com
Next you need to update the 'Server path'. The way that it was configured is based on the MobileMe configuration and it needs to be updated to the iCloud. The value that MobileMe has is /principals/users/1.XXXXXXXXXX/
(The XXXXXXX is the dedicated number for your account. Update the path to /XXXXXXXXXX/principal/
Update the 'Port' to 443 and select the 'Use SSL' option if is not selected.
Restart iCal in Snow Leopard. The Calendar will refresh.
I haven't tested this one, although it looks very similar to the hoops you have to jump through sometimes when running the iCal service in OS X Server.
I'm one of those poor folks maintaining a mixed Lion/Snow Leopard setup holding out for some kind of update to Snow Leopard that will support a few basic iCloud functions like this. And I'm not switching from MobileMe to iCloud until either I see that, or have no other choice next Summer.]