2 different font sizes in the same label

You could do this with some jQuery added to your page template. It will replace the label HTML with a new string.

<script type="text/javascript">
jQuery.noConflict();
  jQuery(document).ready(function($) {

     $('#field_2_1 label').html('<span class="biglabel">this font is bold and big</span> and this is not');

  });
</script>

You just need to replace the "field_2_1" with the proper id from the containing list item.

Once you've got the new span/class in there, you can style it any way you like.