Do you want to just display an image?
you wouldnt really need "AJAX" for that.. just regular ol' javascript
function display_content(img, alttag){
document.getElementById('content').innerHTML = "<img src=\"" + img + "\" alt=\""+alttag+"\" />";
}
display_content("strategyindex.jpg", "Strategy Index");
Or if you put a <img src="strategyindex.jpg" alt="Strategy Index" /> inside that html file it should load it up
But you do need to define the XMLHttprequest and stuff, like the person before me said
(i wrote this in this little box, so the quote syntax might be a bit off, not sure )