Okay, so the idea is that when the person rolls over "Americas" then the stock chart for "Americas" appears. Ditto for "Europe" and "Asia". Right??
But *WHY* do you then want to REVERT BACK to the prior image when you mouse off one of the words??? Why not just leave the current stock there, as is??
So why do we need any "image map"? Why can't we just use <span>s and be happy? And what is the URL of the third graph??? I can't demo the code to you with only the two images.
Incidentally, your page there has a virus. When I right-clicked and downloaded the image file (HP_NKY.png), it also tried to hand me a Trojan virus that my virus scan software detected and killed.
You need to clean up that page and/or site, it would seem.