Hi,
It can be done using a custom product listing which will generate the appropriate HTML with the four thumbnails (or less.. or more).
The trick is that, for each product their are four elements and four images. When the mouse move over one element, the background image is changed using the image attached to the targeted element.
jQuery('.images_spacer').mouseover(function () {
jQuery('.imgrow-'+jQuery(this).attr('rev')).html( jQuery(this).html() );
});
For the rest, it is HTML and CSS.
Regards,