IF you are running Toad for Oracle on Windows 7 and you're getting the error: "Can't initialize OCI. Error -1", when you're trying to initiate a connection, THEN go to the "Properties" of the Toad shortcut in the Start Menu and in the Compatibility Tab tick the check box next to the text: "Run this program as an administrator." When you run Toad again you would be able to open connections!!
PS: Also make sure your ORACLE_HOME environment variable is set to the correct location. Could be a show stopper in your case like in mine. :-)