if (document.images) {

tab1off = new Image();
tab1off.src = "images/tab1_off.jpg";
tab1on =  new Image();
tab1on.src = "images/tab1_on.jpg";

tab2off = new Image();
tab2off.src = "images/tab2_off.jpg";
tab2on =  new Image();
tab2on.src = "images/tab2_on.jpg";

tab3off = new Image();
tab3off.src = "images/tab3_off.jpg";
tab3on =  new Image();
tab3on.src = "images/tab3_on.jpg";

tab4off = new Image();
tab4off.src = "images/tab4_off.jpg";
tab4on =  new Image();
tab4on.src = "images/tab4_on.jpg";

tab5off = new Image();
tab5off.src = "images/tab5_off.jpg";
tab5on =  new Image();
tab5on.src = "images/tab5_on.jpg";

tab6off = new Image();
tab6off.src = "images/tab6_off.jpg";
tab6on =  new Image();
tab6on.src = "images/tab6_on.jpg";

tab7off = new Image();
tab7off.src = "images/tab7_off.jpg";
tab7on =  new Image();
tab7on.src = "images/tab7_on.jpg";
}

function imageon(imgName){
        if (document.images) {
    document[imgName].src = eval(imgName + 'on.src')
}}

function imageoff(imgName){
        if (document.images) {
    document[imgName].src = eval(imgName + 'off.src')
}}