var xPos = 300;
var yPos = 200; 
var step = 1;
var delay = 30; 
var height = 0;
var Hoffset = 0;
var Woffset = 0;
var yon = 0;
var xon = 0;
var pause = true;
var interval;
img1.style.top = yPos;
function changePos() 
{
        width = document.body.clientWidth;
        height = document.body.clientHeight;
        Hoffset = img1.offsetHeight;
        Woffset = img1.offsetWidth;
        img1.style.left = xPos + document.body.scrollLeft;
        img1.style.top = yPos + document.body.scrollTop;
        if (yon) 
                {yPos = yPos + step;}
        else 
                {yPos = yPos - step;}
        if (yPos < 0) 
                {yon = 1;yPos = 0;}
        if (yPos >= (height - Hoffset)) 
                {yon = 0;yPos = (height - Hoffset);}
        if (xon) 
                {xPos = xPos + step;}
        else 
                {xPos = xPos - step;}
        if (xPos < 0) 
                {xon = 1;xPos = 0;}
        if (xPos >= (width - Woffset)) 
                {xon = 0;xPos = (width - Woffset);   }
        }
        
        function start()
         {
                 img1.visibility = "visible";
                interval = setInterval('changePos()', delay);
        }
        function pause_resume() 
        {
                if(pause) 
                {
                        clearInterval(interval);
                        pause = false;}
                else 
                {
                        interval = setInterval('changePos()',delay);
                        pause = true; 
                        }
                }
        start();