Jquery If radio button is checked

Possible Duplicate:
Check of specific radio button is checked

I have these 2 radio buttons at the moment so that the user can decide whether they need postage included in the price or not:

<input type="radio" id="postageyes" name="postage" value="Yes" /> Yes
<input type="radio" id="postageno" name="postage" value="No" /> No

I need to use Jquery to check if the 'yes' radio button is checked, and if it is, do an append function. Could someone tell me how I'd do this please?

Thanks for any help

edit:

I've updated my code to this, but it's not working. Am I doing something wrong?

<script type='text/javascript'>
// <![CDATA[
jQuery(document).ready(function(){

$('input:radio[name="postage"]').change(function(){
    if($(this).val() == 'Yes'){
       alert("test");
    }
});

});

// ]]>
</script>