lightbox2?

nothing built in - but you can easily override the theme_imceimage_theme() function in your phptemplate file to support lightbox or other similar module

function phptemplate_imceimage_image($s, $w='', $h='', $a='', $id='') {
  $s = 'src="' . $s . '" ';
  $w = isset($w)?'width="'.$w.'" ':'';
  $h = isset($h)?'height="'.$h.'" ':'';
  $a = 'alt="'. $a .'";
  $id = isset($id)? 'id="'. $id .'" ':'';
  $c = 'class="lightbox"'; //lightbox support - check the class name that lightbox wants this to be..
  return "<img ". $s . $w . $h . $a . $id . $c .">";
}