input.setSelectionRange( 2 , 4 );

function setSelectionRange(element, start, end)
{
  if(end === undefined) end = start;

  // firefox
  if("selectionStart" in element)
  {
    element.setSelectionRange(start, end);
    element.focus(); // to make behaviour consistent with IE
  }
  // ie win
  else if(document.selection)
  {
    var range = element.createTextRange();
    range.collapse(true);
    range.moveStart("character", start);
    range.moveEnd("character", end - start);
    range.select();
  }
}