Adding a JQuery Script to the subscription plugin

All i want to do is reference a JQuery script that would allow me to create a popup success message when the submit button has been pressed(for the Subscription widget). I realize i need to go into the Subscription.php file and add an action but i’m not sure where. Here is a link to my site below. Thank you for any responses 🙂

BudgetDr.com

http://wordpress.org/plugins/jetpack/