This is a fairly well known problem. A lot of these had solder problems with the video card. This is a very difficult repair and requires a component level tech. To work around the problem I would open it up and use some canned air to clean the fans and vents as much as possible. Here's some links to other answers on this problem:
http://www.ifixit.com/Answers/View/7248/There+are+vertical+lines+in+my+screen.
http://www.ifixit.com/Answers/View/16344/replace+logic+board+with+core+duo