Buttonset does not work anymore after adding div's - jquery-ui

Question

With succes I've created a page that uses the set of radio buttons that are formatted jquery. But as soon as I add the div's need to position the content on the page, the radio buttons are still formatted, but do not act as radio buttons anymore (they act like checkboxes). This is my code, what's wrong with it?
<script>
$(document).ready(function() {
$("#dt_hel").buttonset();
});
</script>
<!-- end script radiobuttons -->
<div class="demo">
<div id="ContentContainerLeft" >
<form id="dt_this_form" name="dt_this_form" action="this.php" method="post">
<p>
</div>
<div id="ContentContainerMiddle" >
<P>
<div id="dt_hel" style="font-size:80%;">
<input type="radio" id="radio1" name="dt_hel" value="0" /><label for="radio1">Lower</label>
<input type="radio" id="radio2" name="dt_hel" value="1" /><label for="radio2">Equal</label>
<input type="radio" id="radio3" name="dt_hel" value="2" checked/><label for="radio3">Higher</label>
</div>
<P></P>
</div>
<div id="TweetContainer" >
<P>
</div> <!-- end tweetcontainer -->
</div><!-- End demo -->
</form>

Answer 1

If you follow the rule of closing the most recent tag before closing older tag (ie set the form opening tag above the tag) then it should work e.g.
<form id="dt_this_form" name="dt_this_form" action="this.php" method="post">
<div class="demo">
<div id="ContentContainerLeft" >
<p>
</div>
<div id="ContentContainerMiddle" >
<P>
<div id="dt_hel" style="font-size:80%;">
<input type="radio" id="radio1" name="dt_hel" value="0" /><label for="radio1">Lower</label>
<input type="radio" id="radio2" name="dt_hel" value="1" /><label for="radio2">Equal</label>
<input type="radio" id="radio3" name="dt_hel" value="2" checked/><label for="radio3">Higher</label>
</div>
<P></P>
</div>
<div id="TweetContainer" >
<P>
</div> <!-- end tweetcontainer -->
</div><!-- End demo -->
</form>