If a broken image is coming up when the mouse moves over it in IE, then the problem is that the images are not in the location that is specified - are all of the images in the same directory as the html file?
After exporting the HTML and images from fireworks, open the exported HTML file into IE and see if it works (it should).
When you insert the exported HTML into the webpage, did you move the generated images into an 'images' directory (or similar) - if so then there is the problem: FPage will update the links for the standard images, but can't update the javascript for the mouseovers. If this is the problem, then you will need to edit the HTML code: find the javascript that handles the mouseover images, and check all the paths are correct.