if (document.images) {            
            img1on = new Image();   img1on.src = "http://www.ihrc.fiu.edu/lcr/images/nav/research_subon.gif"; 
            img2on = new Image();   img2on.src = "http://www.ihrc.fiu.edu/lcr/images/nav/data_subon.gif";  
            img3on = new Image();   img3on.src = "http://www.ihrc.fiu.edu/lcr/images/nav/people_subon.gif";
            img1off = new Image();  img1off.src = "http://www.ihrc.fiu.edu/lcr/images/nav/research_suboff.gif"; 
            img2off = new Image();  img2off.src = "http://www.ihrc.fiu.edu/lcr/images/nav/data_suboff.gif";
            img3off = new Image();  img3off.src = "http://www.ihrc.fiu.edu/lcr/images/nav/people_suboff.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");        
            }
    }