I can't log in in Wow

Hi, I'm a new player and I downloaded WoW. I entered WoW ( WOTLK ) and entered my ID ( not e-mail address ) and password. It said " Connect, Authenticating ( or something )" then it showed me an errorr saying " The information you have entered is not valid. Please check the spelling of the account name and password. If you need help in retrieving a lost or stolen password and account, see [www.worldofwarcraft.com/loginsupport] or more information."
I have Battle.net installed by the way... What can I do ? Please, help!