Nice idea, you could use this too:
Code:
<div id="postcount"></div>
<script type="text/javascript">
var posts;
for (posts=0;posts<$post[posts];posts+=100)
{
document.getElementById("postcount").innerHTML=document.getElementById("postcount").innerHTML + "<img src='image.gif' />";
}
</script>
This way you wouldn't need the conditionals, members with more than 800 posts wouldn't stay in level 5 and you'd only need 1 image.