"when you create the recordset for the entered username, does it lookup the username from a db table"
yes, the idea is to create a recordset that looks up the entered username to see if it exists in the table
"how does the entered username get inserted into the db table?"
when the user registers, it stores the user name in the table
if you need help configuring this, I suggest a premiere support appointment:
http://www.webassist.com/premier_request.php