<script>
 function numberOnly()
 {
  if (
   (
    (event.keyCode==190) || (event.keyCode>=96 && event.keyCode<=105) || (event.keyCode==110)
    || (event.keyCode>47 && event.keyCode<58) || event.keyCode==8 || event.keyCode==16
    || event.keyCode==116 || event.keyCode==18 || event.keyCode==9
    || (event.keyCode>=37 && event.keyCode<=40) || event.keyCode==46
   ) == false
   )
  {
   event.returnValue=false;
  }
 }

 var tmpNC="";
 function numberComma(obj)
 {
  if(tmpNC==obj.value) return;
  tmpNC=obj.value;
  obj.value=numberComma2(tmpNC);
 }
 function numberComma2(s)
 {
  s=s.replace(/\D/g,"");
  l=s.length-3;
  while(l>0) {
   s=s.substr(0,l)+","+s.substr(l);
   l-=3;
  }
  return s;
 }
</script>

<input onKeyDown=JavaScript:numberOnly(); onKeyUp=JavaScript:numberComma(this);>