how to open an alert box when a user enter his email id twice in email field

i m using this plugin in my site.my problem is that i realy need another condition that the user couldn’t fill the form more than once means he could not fill his email again.and in the field name college name if there are 10 entries in the field with same college name.then a popup should appear that sorry .

http://wordpress.org/extend/plugins/wordpress-form-manager/