var bg = new Image();
bg.src = 'images/background.jpg';
var tab1 = new Image();
tab1.src = 'images/tab1.gif';
var tab2 = new Image();
tab2.src = 'images/tab2.gif';
var tab3 = new Image();
tab3.src = 'images/tab3.gif';
var tab4 = new Image();
tab4.src = 'images/tab4.gif';