mouseover producing multiple images works in Firefox, but not i.e

The code below allows the user to hover over 1 object and it not only replaces the object but also shows an additional object between the buttons.

It works great in Firefox, but does not in Internet Explorer.

HELP

webpage: http://www.isp.ucar.edu/

Thx, Terri

if ( < document.images) {

    img1on = new Image();
    img1on.src = "images/buttons/button-beachon-on.gif";
    img1off = new Image();
    img1off.src = "images/buttons/button-beachon.gif";

    img2on = new Image();
    img2on.src = "images/buttons/button-bgs-on.gif";
    img2off = new Image();
    img2off.src = "images/buttons/button-bgs.gif";

    img3on = new Image();
    img3on.src = "images/buttons/button-iam-on.gif";
    img3off = new Image();
    img3off.src = "images/buttons/button-iam.gif";

    img4on = new Image();
    img4on.src = "images/buttons/button-nvia-on.gif";
    img4off = new Image();
    img4off.src = "images/buttons/button-nvia.gif";

    img5on = new Image();
    img5on.src = "images/buttons/button-utls-on.gif";
    img5off = new Image();
    img5off.src = "images/buttons/button-utls.gif";

    img6on = new Image();
    img6on.src = "images/buttons/butt开发者_StackOverflowon-water-on.gif";
    img6off = new Image();
    img6off.src = "images/buttons/button-water.gif";

    img7on = new Image();
    img7on.src = "images/buttons/button-exploratory-on.gif";
    img7off = new Image();
    img7off.src = "images/buttons/button-exploratory.gif";


    // second image that does not appear in original button space
    img1ad = new Image();
    img1ad.src = "images/buttons/beachon-overview-sm.gif";

    img2ad = new Image();
    img2ad.src = "images/buttons/bgs-overview-sm.gif";

    img3ad = new Image();
    img3ad.src = "images/buttons/iam-overview-sm.gif";

    img4ad = new Image();
    img4ad.src = "images/buttons/nvia-overview-sm.gif";

    img5ad = new Image();
    img5ad.src = "images/buttons/utls-overview-sm.gif";

    img6ad = new Image();
    img6ad.src = "images/buttons/water-overview-sm.gif";

    img7ad = new Image();
    img7ad.src = "images/buttons/exploratory-overview-sm.gif";
}

function imgOn(imgName) {
    if (document.images) {
        document[imgName].src = eval(imgName + "on.src");
        document["holder"].src = eval(imgName + "ad.src");
    }
}

function imgOff(imgName) {
    if (document.images) {
        document[imgName].src = eval(imgName + "off.src");
        document["holder"].src = "images/buttons/isp-overview-sm.gif";
    }
}

First of all, eval in these functions are totally uncalled for

function imgOn(imgName) {
    if ( < document.images) {
        document[imgName].src = eval(imgName + "on.src");
        document["holder"].src = eval(imgName + "ad.src");
    }
}

function imgOff(imgName) {
    if ( < document.images) {
        document[imgName].src = eval(imgName + "off.src");
        document["holder"].src = "images/buttons/isp-overview-sm.gif";
    }
}

They should read

function imgOn(imgName) {
    document.getElementById(imgName).src = window[imgName + "on"].src;
    document.getElementById("holder").src = window[imgName + "ad"].src;
}

function imgOff(imgName) {
    document.getELementById(imgName).src = window[imgName + "off"].src;
    document.getElementById("holder").src = "images/buttons/isp-overview-sm.gif";
}

And instead of multiple img1on = new Image(); followed by calls to window[foo] you should do this

var myImages = {};
myImages["img1on" = new Image();

Then you can later on do

var foo = myImages[imgName + "on"].src;

to get the src.