Is there a specific jquery you have in mind that throws a window to cover up the entire screen space, remembers the response of the user and is customizable?
I tried the openmodal jquery but could not get it to work!!
jquery popups should be a simple task to implement. Should just be a matter of including the .js and css file after the jquery reference. Then it should work. If not you can post your error messages in the javascript thread and the guys there should be able to help you get it working.
That being said, I have seen a lot of sites just do it with a simple javascript alert() message. And it works fine. So it is up to you how you approach it, but there is no need to get really fancy, but would not hurt if you did.