1) Dreamweaver will use virtual() instead of require_once() if the Create Links Relative To option is set to Site. Before running form builder, try changing that to Document,
2) CSS Form Builder will Create the CSS Form. You will need to add the functionality using SecurityAssist or Dreamweaver's Authenticate user Behavior to make the forms created by form builder function.
3) Is the Preview turned off? Go to Edit -> WebAssist Preferences. In the preview section check then uncheck the disable preview option and click OK.