[jQuery] Am I missing something dumb?

I am a newbie (and very much a convert) to JQuery but have spent all
afternoon bashing my head against a brick wall with this one.

I want to show hide (or in the example, change the class) of a single
element in an array of DIV's).

Whatever I do, I can only reference the first one, and the others seem
to be ignored (even though they appear to resolve to objects).

I have narrowed my code down into a near little example. I am using
version 1.1.3.1


Cheers in advance.


JJ



<SCRIPT language=javascript src="jquery.js"></SCRIPT>
<style>
.selected
{
font: 12px Arial, Helvetica, sans-serif;
color: #FF0000;
}
</style>


<DIV class='wump1' id=SB1>aaaa</DIV>
<DIV class='wump1' id=SB1>bbb</DIV>
<DIV class='wump1' id=SB1>ccc</DIV>
<DIV class='wump1' id=SB1>ddd</DIV>

<script>
$(document).ready(function()
{

        $("#SB1:nth(1)").addClass("selected")
        $("#SB1:nth(0)").addClass("selected")

})
</script>