Show announcement on the site
You can use jQuery for the this purpose. Simply use mouseover event on the  announcement DIV. Write a jQuery function to hide this DIV using .hide method of jQuery. like this.

$(document).ready(function() {
$("#announcement_div_id").hover(function() {
$("#announcement_div_id").hide();
});
});


Here announcement_div_id is the id of the div which you want to hide.