credo tu voglia fare
codice:
<select name="sesso" onchange="mostra(this.options[this.selectedIndex].text.toLowerCase());">
<option value="">------</option>
<option value="M">Uomo</option>
<option value="F">Donna</option>
<option value="C">Coppia</option>
</select><span id="uomo" style="display:none;">  [img]img/male.gif[/img]</span><span id="donna" style="display:none;">[img]img/female.gif[/img]</span><span id="coppia" style="display:none;">[img]img/couple.gif[/img]</span>

<script>


function mostra(nr) {
if(document.getElementById(nr)){
var text=document.getElementById(nr);
if (text.style.display=="none") {
text.style.display="inline";
}else{
text.style.display="none";
}
}
}
</script>