I think most people are going into this topic with the same problems, myself included! You've said it yourself, it is such a broad question, there's really no straight-forward answer.
Here's what I've taken away from it all, I'm not saying it's right but I hope it helps!
History needs Memory and Memory needs History. One can't exist without the other. History will always be influenced in some way by memory and vice versa. History will always claim to be more accurate then human memories, as it is recorded fact, but memory will always include the actual feelings and emotions of that event.
The problem with the Smithsonian website though is that it's too one sided. It shows a lot of bias and a lot of memory, but not as many historical facts. Sure it has pictures and videos and external links, but the main content of the website itself is based on memory. The title of the opening page is even 'Remembrance and Reflection'!
I think our arguments have to say something like without memory, there is no history and without memory, history doesn't make sense. We'll have to try to show that the Smithsonian website shows this, and find a related text that explores the interplay and individuality of the two! Then on top of all that information, we'll have to link it back into the question, and make it relevant.
The module itself is looking at Representation in texts, so what we really need to do is explore the representation of the September 11 attacks through the Smithsonian website, AND do the same with the event our related text and show the similarities between the two.
Hope this helps, and if not check out the link below. Good luck!
http://cherylsenglishspace.wikispaces.com/HSC+Adv+Mod+C+History+&+Memory