var step_ratio = 0.1;
objs = new Array();
objs_x = new Array();
objs_y = new Array();

function addfollowmark(name, x, y) {
i = objs.length;
objs[i] = document.getElementById(name);
objs_x[i] = x;
objs_y[i] = y;
}

function followmark() {
for(var i=0; i<objs.length; i++) {
var fm = objs[i];
var fm_x = typeof(objs_x[i]) == 'string' ? eval(objs_x[i]) : objs_x[i];
var fm_y = typeof(objs_y[i]) == 'string' ? eval(objs_y[i]) : objs_y[i];
if (fm.offsetLeft != document.body.scrollLeft + fm_x) {
var dx = (document.body.scrollLeft + fm_x - fm.offsetLeft) * step_ratio;
dx = (dx > 0 ? 1 : -1) * Math.ceil(Math.abs(dx));
fm.style.left = fm.offsetLeft + dx;
}
 var diffY;
 if (document.documentElement && document.documentElement.scrollTop)
 diffY = document.documentElement.scrollTop;
else if (document.body)
 diffY = document.body.scrollTop;
 
if (fm.offsetTop != diffY+ fm_y) {
var dy = (diffY+ fm_y - fm.offsetTop) * step_ratio;
dy = (dy > 0 ? 1 : -1) * Math.ceil(Math.abs(dy));
fm.style.top = fm.offsetTop + dy;
}
fm.style.display = '';
}
}

addfollowmark("ad_01", 1, 5);
addfollowmark("ad_02", "document.body.clientWidth-101", 5);
//addfollowmark("ad_03", 1, 310);
addfollowmark("ad_04", "document.body.clientWidth-101", 310);

setInterval('followmark()',20);