MyImages=new Array();
    MyImages[0]='imagens/random/banner_1.jpg';
    MyImages[1]='imagens/random/banner_2.jpg';
    MyImages[2]='imagens/random/banner_3.jpg';
    MyImages[3]='imagens/random/banner_4.jpg';
	MyImages[4]='imagens/random/banner_5.jpg';
	
    function newImage()
    {
        document.getElementById("mainImage").setAttribute("src", MyImages[Math.round(Math.random()*4)])
    }