$a="Just to say Hello world. and nothing more!";
$b="Oops! Hello world. rr and thats all";
// try to found
$x= 0 ; $y= 0  ; $xl=strlen($a)- 1 ; $yl=strlen($b)- 1 ;
$k=levenshtein($a,$b);
for($i= 0 ;($i< 6 ) && ($k> 1 );$i++) { // я боюсь отпускать ее больше :)
  while (TRUE) {
     $x++ ; $kcur=levenshtein(substr($a,$x,$xl-$x),
                              substr($b,$y,$yl-$y));
     if ($k>=$kcur) $k=$kcur  ;
     else { $x-- ; break ; }
  }
  while (TRUE) {
     $y++ ; $kcur=levenshtein(substr($a,$x,$xl-$x),
                              substr($b,$y,$yl-$y));
     if ($k>=$kcur) $k=$kcur  ;
     else { $y-- ; break ; }
  }
  while (TRUE) {
     $xl-- ; $kcur=levenshtein(substr($a,$x,$xl-$x),
                              substr($b,$y,$yl-$y));
     if ($k>=$kcur) $k=$kcur  ;
     else { $xl++ ; break ; }
  }
  while (TRUE) {
     $yl-- ; $kcur=levenshtein(substr($a,$x,$xl-$x),
                              substr($b,$y,$yl-$y));
     if ($k>=$kcur) $k=$kcur  ;
     else { $yl++ ; break ; }
  }
// let's substr common part's
  $sub = $x;
  while ($a{$x}==$b{$y}) {$x++;$y++;}
  $substr[]=substr($a,$sub,$x-$sub); 
}
echo substr($a,$x,$xl-$x)."<br>";
echo substr($b,$y,$yl-$y)."<br>";
echo $k."<br>";
print_r($substr);

$a="Just to say Hello world. and nothing more!";
$b="Oops! Hello world. rr and that's all";
// try to found
$x=0; $y=0 ; $xl=strlen($a)-1; $yl=strlen($b)-1;
$substr=array();
$k=2;
while(($x<$xl)&&($y<$yl)&&($k>1)) {
  $k=levenshtein(substr($a,$x),substr($b,$y)) ;
  while ($x<$xl) {
     $x++ ; $kcur=levenshtein(substr($a,$x),
                              substr($b,$y));
     if ($k>=$kcur) $k=$kcur  ;
     else { $x-- ; break ; }
  }
  while ($y<$yl) {
     $y++ ; $kcur=levenshtein(substr($a,$x),
                              substr($b,$y));
     if ($k>=$kcur) $k=$kcur  ;
     else { $y-- ; break ; }
  }
// let's substr common part's
  $sub = 0;
  while ($a{$x+$sub}==$b{$y+$sub}) {$sub++;}
  if ($sub>0)
    $substr[]=array('ax'=>$x,'bx'=>$y,'len'=>$sub,
                    'field'=>substr($a,$x,$sub));
  $x+=$sub ;$y+=$sub;
}
echo "<pre>";
print_r($substr);
echo "</pre>";