First create the pages using Security Assist.
then modify the form using form builder.
See the "Modifying an existing form with CSS Form Builder" tutorial on the how to section of the form builder support page:
for information on adding validation see the following:
Using CSS Form Builder -> Editing Group Contents -> Customizing a set's error message in the help documentation:
If you are getting an error message, please post the exact text of the error so we can have an iddea of what is going wrong.