I have developed a website that works perfectly in IE6, Safari 5, and Firefox 3, but is totally unstable in IE 7 and 8.
(See, for example, www.andynic2.eu and then click "Sculpture and Paintings".)

Each html file, which contains some javascript functions, passes validation on the W3 validator. The heading in each file is:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">

Any idea what I need to do to get the application to work correctly in IE7 and 8?

Thanks for your help,