function wbggchangePos() {  
      width = document.body.clientWidth;  
      height = document.body.clientHeight;  
      Hoffset = ad.offsetHeight;  
      Woffset = ad.offsetWidth;  
      ad.style.left = xPos + document.body.scrollLeft; 
      ad.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 wbggstart() {  
      ad.visibility = "visible";  
      interval = setInterval("wbggchangePos()", delay);  
    }