links in navigation panel

hi,

can anyone tell me how to enable links in navigation panel in enterprise portal. ie., in navigation panel, suppose we have, yahoomail, rediffmail.... etc.. if we click on yahoomail, it must open that link in content area of portal.... can any one tell me... how to do this....& pls send ur reply to my mail-id: mail2lakvi@yahoo.co.in

thanks & regards

vijaya lakshmi