[Seven Skins]

Have you tried radio buttons?

<label><input type="radio" name="userfield[field7_set]" checked>Yes</label>
<label><input type="radio" name="userfield[field7_set]">NO</label>

Or May be this:

<div class="blockrow">
  <ul class="checkradio group">
    <li>
    <label for="repdisplay">{vb:rawphrase repdisplay}:</label>
      <select class="primary" name="userfield[field7]" id="cfield_7" tabindex="1">
      <option value="1" selected="selected">Yes</option>
      <option value="0">No</option>
      </select>
    <input type="hidden" name="userfield[field7_set]" value="1" />
    </li>
  </ul>
</div>