yum repository help

Hi,
I've got what is probably a pretty silly question: I'm trying to attach to the "main" Red Hat yum repository using the subscription manager utility under sudo. sudo asks for my system password, which it accepts happily. The Subscription manager then asks for my Username and password. It seems to accept neither my system credentials, (as expected,) nor my Red Hat account credentials. Is there some other set of credentials I need? Where can I find them?

Thank you for your help,

Dan Bush.