var i1 = new Image();
var i2 = new Image();
var i3 = new Image();
var i4 = new Image();

i1.src = 'images/approach_over.gif';
i2.src = 'images/practitioners_over.gif';
i3.src = 'images/links_over.gif';
i4.src = 'images/contact_over.gif';