After entering your username and password at the login window in Mac OS X v10.6 Snow Leopard, you may see this alert: "The system was unable to unlock your login keychain" (With three buttons: "Continue login", "Create New Keychain", "Update Keychain Password".) This may happen if you changed your login keychain password or user password (so they are now different passwords), while started from the Mac OS X v10.6 Install DVD.