This isn't pretty, but I think you'll get what I'm trying to do.

<label><input name="jpgSel" type="radio" value="0">jpg 1</label><br />
<label><input name="jpgSel" type="radio" value="1">jpg 2</label><br />
<div id="showjpg"></div>

and

$(document).ready(function() {
    $("select").change(function () {
           if ($("jpgSel:checked").val() == 1) {
            $('#showjpg').attr({
                src: 'one.jpg',
                 alt: 'one dot jpg'
        });
    }
    else {
            $('#showjpg').attr({
                 src: 'two.jpg',
                 alt: 'two dot jpg'
        });
    }
});