In jQuery, how do I select an element by its name attribute?

another way

$('input:radio[name=theme]').filter(":checked").val()

To determine which radio button is checked, try this:

$('input:radio[name=theme]').click(function() {
  var val = $('input:radio[name=theme]:checked').val();
});

The event will be caught for all of the radio buttons in the group and the value of the selected button will be placed in val.

Update: After posting I decided that Paolo's answer above is better, since it uses one less DOM traversal. I am letting this answer stand since it shows how to get the selected element in a way that is cross-browser compatible.

This should do it, all of this is in the documentation, which has a very similar example to this:

$("input[type='radio'][name='theme']").click(function() {
    var value = $(this).val();
});

I should also note you have multiple identical IDs in that snippet. This is invalid HTML. Use classes to group set of elements, not IDs, as they should be unique.

$('input:radio[name=theme]:checked').val();