You don't need to use SQL if you just want to pick up the user's username from the core properties. Check out DSTrainingForm over at www.betasprings.com (please use host / dnnhost to log in). You'll see username, firstname, lastname, and email displaying the account info because they were linked to the core properties in Manage Questions, Advanced Field Properties. (You'll get there if you click on the little pen icon beside the field.).
Is this what you're trying to accomplish?
Candace