var floatingDiv;
var screenWidth;
var instanceAlready = false;

var horizontalMovement = 1;

function startTimer(id) {

	if(instanceAlready)
	{
		return;
	}
	else
	{
    		floatingDiv  = document.getElementById(id);
    		screenWidth  = document.body.clientWidth;
		instanceAlready = true;

   	    	window.setInterval("moveDiv()", 1);
	}
}

function moveDiv() {
    var currentLeft = floatingDiv.offsetLeft;

    if (currentLeft < 0) {
        horizontalMovement = 1;
    } else if ( ( currentLeft + floatingDiv.offsetWidth) > screenWidth -6) {
        horizontalMovement = -1;
    }

    floatingDiv.style.left = currentLeft + horizontalMovement + "px";
}