if (document.images) {

img1on=new Image();
img1on.src="../images/inside.on.gif";
img1off=new Image();
img1off.src="../images/inside.off.gif";

img2on=new Image();
img2on.src="../images/portfolio.on.gif";
img2off=new Image();
img2off.src="../images/portfolio.off.gif";

img3on=new Image();
img3on.src="../images/services.on.gif";
img3off=new Image();
img3off.src="../images/services.off.gif";

}

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

function imgOff(imgName) {
        if (document.images) {
            document[imgName].src=eval(imgName + "off.src");
        }
}