var tab_image = new Array(3);
for (var i=0; i< tab_image.length;i++)
	tab_image[i]= new Image();
tab_image[0].src='img/fo/plan_1.gif';
tab_image[1].src='img/fo/plan_2.gif';
tab_image[2].src='img/fo/plan_3.gif';

var n=0;

function change() {
n= ++n;
if (n == tab_image.length) n=0;
window.document.image.src=tab_image[n].src;
}