[Deff]

<style>
  .demoIMG { 
    position:relative; 
    margin:0 auto; 
  }  
    .demoIMG  img.novisible{ 
    position:absolute; 
  } 
  .demoIMG img.novisible {opacity:0;filter:alpha(opacity=0);}
  
  .demoIMG:hover img.novisible{opacity:1.0;filter:alpha(opacity=100);}
  
  .demoIMG:hover img.visible {opacity:0;filter:alpha(opacity=0);}
</style>

<table width=40% border="1"><tr align="center"><td >

<a class="demoIMG" href="#">
<img class="novisible" src="http://javascript.ru/forum/images/smilies/tongue.gif" />
<img class="visible" src="http://javascript.ru/forum/images/smilies/yes4.gif" />
</a>

</td>
<td>

<a class="demoIMG" href="#">
<img class="novisible" src="http://javascript.ru/forum/images/smilies/tongue.gif" />
<img class="visible" src="http://javascript.ru/forum/images/smilies/yes4.gif" />
</a>

</td>
</tr></table>