I would use the perl on the server to create an array or some other structure, as DWS suggests.

I, personally, would do it as follows: 1) Create an image map with numbered regions. 2)Create an array whose index corresponds to the number regions. 3) onmouseover call a function that looks like this:

<element onmouseover="bogus(this);">

function bogus(element) {
    var mouseOver = element + "name";
    var visiElem = document.getElementById(mouseOver);
    visiElem.style.visibility = "visible";
}
[download]

Or something like that.

It is possible to do what you want by using XMLHttpRequests, but the page will only be accessible to NS/Moz and IE5.5/IE6.

I'm sure that if wrote something pretty special, you could cause perl code to be executed through javascript, but it would probably have to be pretty special.