Hi Rick, I haven't used this, but my hunch would be mp_userproperties for newly defined custom properties.
However, there is a FirstName and LastName field on mp_users (I'm using MySQL). Since those were already commented out in the configuration file, I have a feeling it may be using these fields on mp_users. If you have a SQL tool that will let you browse the data, that will be the easiest way to find it on your own, or you could just try querying the fields. If that fails, check mp_userproperties for PropertyName='FirstName'.
Jamie