88160 Need Perl/CGI Script

I have a site with approx 3,000 to 4,000 uniques per day. BUT these unigues are primarily 1 visit per page. The pages in that particular folder are about 30,000 pages. I need a programmer who knows how to make a script that will cause a 2 1/2 by 3 ad slide across each of my pages automatically when someone comes to any one of my pages. Can this be done without having to do search & replace on all the pages? Please post experience at doing this and tell me how you propose to do it and how long to complete project.