Why does my page work in IE9's IE7 mode, but not in IE7 itself?

Question

I recently went live with our new home page, after heavily testing it in each of IE9\'s browser and document modes (not just compatibility mode, but actual IE7 and IE8

Answer 1

Download the free Microsoft Virtual PC and MS's free Hard Drive images containing IE 7, 8, etc... that's why they make these available.

There seems to be a million jQuery slideshow plugins and most are compatible with IE 7.

jCarousel is one and you can change it with CSS to look like what you have now.

This page contains 42 various slide-show plugins.

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EDIT:

I also recommend that the page be brought into W3C compliance before tackling the other issues.