Option Value ?

I want to display some pictures on my html page.I can use it using PROMPT but.I want to do this by using "<select>"<option></select>" but I failed to do it...whats wrong with it ?:confused: here is my code so far..

<script type="text/javascript">

function showselected(){
var yaz=((document.test.test2.selectedindex)+1);
for(m=1;m<=yaz;m++)
{

document.write("<img src='bir.bmp'>"+m);

}}
</script>

<form name="test">
<select name="test2" onChange="showselected()">
<option value=5>Option 5</option>
<option value=10>Option 10</option>
<option value=15>Option 15</option>
</select>
</form>