Thanks again for your prompt reply.
I am creating an elearning course for one of the software. I want to create login screen boxes on the blank slides for entering username and password as we login to any application. So that, while viewing the elearning output, the user get the feel of logging in to the application itself. I think using text entry boxes and adding variables I would be able to add successful or failure pop ups messages on entering right or wrong username and password.
OK, it is not really branching which you want, but checking if the user has put in something in the fields? Validating the entries will be difficult, that is normally a functionality of the LMS. If it is only to test if user understand they have to enter 'anything' in those fields, maybe this could help:
Where is Null? - Captivate blog
Will you deploy the course from a LMS? It is possible that the user variable cpQuizInfoStudentName is populated with the name from the LMS. You have to check, it also depends on the way the LMS-accounts have been set up. Password is a lot more difficult.