Use jQuery. You can use a jQuery Event to detect a click and then hide or show divs.
So, You have a button called "HideDiv" and "DivToHide" is the div you wish to hide.
$("#HideDiv").click(function() {
$("#divToHide").hide();
};
It's that easy. Can't really go in-depth here but check out their tutorials: http://docs.jquery.com/Tutorials or browse this site: http://www.learningjquery.com/category/levels/beginner
jQuery actually comes with ASP.Net MVC, check the scripts folder of a new MVC project and you'll see it in there. This site using jQuery and MVC :) So your browsing a sample of what is possible with it