<style>
#side_block {
left: 10px;
position:fixed; //fixed, не absolute
top:0;
width:100px; // ; в конце строки
}
</style>
<div id="side_block"> <a id="dynamic-to-top" href="ссылка" style="display: inline;">картинка</a></div>
<script type="text/javascript">    
$(function(){    
     $(window).scroll(function() {     
     var top = $(document).scrollTop();    
     if (top > 98) $('#side_block').show();     
     else $('#side_block').hide();    
     });    
});    
</script>

<script type="text/javascript">
$(window).scroll(function() {
  var top = $(document).scrollTop();
  $('#side_block').animate({top: top+'px'});
  if (top > 98) $('#side_block').show();    
    else $('#side_block').hide();
});
</script>