I've been having the same issue. I use iCal as my main "hub" for calendars and use MobileMe as a backup and to sync to my iPhone. I updated to the new MobileMe today and lost ALL of my calendars in iCal. Everything. Fortunately, all of my calendars are still in MobileMe and on my phone, but I want them back on my computer in iCal!
I found this information today and I think it's what I need to solve my issue (hopefully it can help some of you as well)
Important: Do not follow these steps until you have successfully joined the new MobileMe Calendar. For more information about joining the new MobileMe Calendar, see this article.
1) Open iCal Preferences.
2) Click Accounts.
3) Click the plus button at the bottom of the page.
4) For both Description and Username, enter your full MobileMe email address, including @me.com or @mac.com. If you don't include @me.com or @mac.com, the setup will not be successful.
5) Enter your MobileMe password.
6) Click the disclosure triangle next to Server Options.
7) For Account URL, enter the following without quotes: "https://cal.me.com". Be sure to include the full URL, including the "https://". Note that you do not need to include a closing "/" at the end of the url.
8) Click Add.
Now that your MobileMe account is set up, iCal will begin downloading the data from the new MobileMe Calendar servers.
http://support.apple.com/kb/HT4330
So all of this seems like what I need, but I'm still having an issue adding my calendar. When I go to add my MobileMe account into iCal, a Login Failed message pops up that says "Your password was rejected by the server cal.me.com for the login Rachael" Does that mean my password is incorrect? Because it's not. Any suggestions?
Thanks!