To sync your Yahoo! Calendar with Apple's iCal (if you're using Apple's Leopard OS (10.5) or later):

1. Open iCal.
2. Click the iCal menu and select Preferences.
3. Click Accounts.
4. Click the + sign on the bottom-left to setup a new account.
5. Select Yahoo! from the Account type drop-down.
6. Enter your Yahoo! ID in the corresponding ID field.
7. Enter your Yahoo! password in the password field.
8. Click Create.
9. In the next window, choose the frequency that iCal will sync with Yahoo! Calendar.

Your Yahoo! Calendar events will begin to show up in iCal when the next sync occurs.