function DN_System_Scroll(){
this.type = -1; this.intval = 0;
}
DN_System_Scroll.prototype.step = function(){
 var y = ((this.type == 1) ? document.documentElement.scrollTop : document.body.scrollTop), step = 25;
 y -= Math.ceil(y * step / 100);
 y = (y < 0) ? 0 : y;
 if(this.type == 1){
   document.documentElement.scrollTop = y;
 } else {
   document.body.scrollTop = y;
 }
 if(y == 0){
  clearInterval(this.intval); this.intval = 0;
 }
}

DN_System_Scroll.prototype.begin = function(){
 if(this.intval == 0){
  if(document.documentElement && document.documentElement.scrollTop) {
   this.type = 1;
  } else if (document.body && document.body.scrollTop){
   this.type = 2;
  } else {
   this.type = 0;
  }
  if(this.type > 0){
   this.intval = setInterval('SCROLL.step()',50);
  }
 }
}

var SCROLL = new DN_System_Scroll();