I have an application external from SFDC written in html/Javascript that needs to be able to query lead information for a specified sales rep within SFDC.  I am looking at the AJAX Developers toolkit but I am having problems creating the connection and loging in.  I have included <script src="/soap/ajax/20.0/connection.js" type="text/javascript"></script> in my javascript code, but continue to receive error  "Error: System error: -2146697211." when trying to issue the login command formatted as

var result = sforce.connection.login("xxx-id", "xxx-password");

What is needed to create a connection and login thru javascript