>>671
<?php

$strValue = '<a href="URN:ISBN:12-3456-7890-1">hoge</a>';
$strUrl = 'http://www.amazon.co.jp/exec/obidos/ASIN/';
$strPattern = "/URN:ISBN:([0-9]{2})-([0-9]{4})-([0-9]{4})-([0-9])/i";
$strValue2 = preg_replace( $strPattern, $strUrl."$1$2$3$4",$strValue);

print $strValue2;

?>