Construisez un site Web

whe have i web site whit joomla 2.5 we used a profoms plugin for i on line application we need to add a simple input text area in the form that when the user click in to input is answer it will apear an info text but this text will not appear in the form exemple of what we need [login to view URL] on the bottow the question :Numéro d'assurance sociale