If you are wanting to get more than one user on at a time, you will need to parameterize logins. Gather a list of usernames and passwords for each user if it is a "app local login" (you have to enter a UN and PASS) and create a parameter for each ... the below link details this pretty well, and avoids me having to type it all out :)
http://motevich.blogspot.com/2007/11/loadrunner-parameter-parameterization.html
