Sorry for the double post, please merge with the above one. Everyone here is the Shawn's Premium Membership Popup. I got it to show by logging out and logging back in...therefore i had to change my password because it expired.
Just create a div with the content, and hide/show it using javascript and a cookie - find out what time-span you want (say 1 week) and put the cookie on a 1 week timeout - if it's timed out, show the div as an absolute-positioned div hovering above other content - it's not really hard, and there are thousands of these out there on the web. Do a Google-search.