mysql username and password

in the pro version of virtualmin, what would the username for a sub server be?

I am trying to install "wordpress MU" and it is asking for the database name = wordpress username = username password = password database host = localhost

do I need to create a database named word press first? I know the script installer of wordpress installs into the correct mysql database.

I assume the username and password is the virtual server user and pass, but this is a sub server of that account, shouldn't it have a different username, or is that not important?