I believe the code you are editing here is a part of the Dreamweaver recordset, not the data assist insert.
in the data assist insert behavior, when you bind a column to a form value, it will show code similar to this in the value section:
<?php echo((isset($_POST["textfield"]))?$_POST["textfield"]:"") ?>
you would want to edit that code to use the ucwords() function:
<?php echo((isset($_POST["textfield"]))?ucwords($_POST["textfield"]):"") ?>