Modal Popup (possibly iFrame) with AJAX

I need to create a modal popup box that appears when a site is visited (with the background inactive and grayed out. The popup will have 4 logos that let the visitor select a site. A text description below the logos will change according to which logo the visitor hovers over. Additionally, a checkbox gives the visitor the option to remember which site they selected the next time they come to this page. Clicking outside the box will close the popup leaving the page behind it. Please explain how you are going to do this, which plugin or script you will use, and what your time frame is.