var x = 50, y = 60
var xin = true, yin = true;
var step = 1;
var delay = 15;

var obj;
var L, T, R, B;

function floatAD(){
	obj.style.left = x + document.body.scrollLeft + 'px';
	obj.style.top = y + document.documentElement.scrollTop + 'px';

	x = x + step*(xin ? 1 : -1);
	if (x < L) { xin = true; x = L }
	if (x > R){ xin = false; x = R }

	y = y + step*(yin ? 1 : -1);
	if (y < T) { yin = true; y = T }
	if (y > B) { yin = false; y = B }
}

function initFloatAd(id){
	obj = document.getElementById(id);
	if(obj){
		L = T = 0;
		R = document.body.clientWidth - obj.clientWidth;
		B = document.documentElement.clientHeight  - obj.clientHeight;
		itl = setInterval("floatAD()", delay);
	}
}