[rushed]

try this

 alter table users add donorstar enum('yes,'no') NOT NULL DEFAULT 'yes';

$str .= ($user['donor'] == 'yes' && $user['donorstar'] == yes ? '<img src="'.$image_dir.'donor.png" alt="" title="" />' : '');

print ("<tr>
<td class='rowhead_form' align='center'>Hide donor star</td>
<td class='rowhead' align='left'>
<input type='radio' name='donorstar' value='yes'".($CURUSER["donorstar"] == "yes" ? " checked='checked'" : "")." />Yes
<input type='radio' name='donorstar' value='no'".($CURUSER["donorstar"] == "no" ? " checked='checked'" : "")." />No
</td></tr>");

if (isset($_POST["donorstar"]) && ($donorstar = $_POST["donorstar"]) != $CURUSER["donorstar"]) {
                $updateset[] = "donorstar= ".sqlesc($donorstar);
                }