Multi-dimensional Arrays With Image Rollovers

I'm trying to get rollover images to work that are a little more complex than usual. I have a webpage that presently gives information on four groups within an organization. I've put each group within its own div with an id. The div contains a short description of what the group does, thumbnails pictures of each member of the group, and to the right of these thumbnails, a larger picture. This larger picture is supposed to change, when ever the mouse is over a thumbnail to a normal size picture of the thumbnail, for the first part.

I tried to put in a script that will preload all the original images that should be changed. First I created an array with all the names of the divs, then used two for loops, one nested inside the other to get the pictures into the array. Tried to get the names of the array to hold the pictures from the first array with the names (inames), using a two dimensional array (used an example from a post on this forum) but it seemed to have gone astray, as the onmouseover doesn't work. Code: