Código PHP:
<?php
$texto = str_replace ( "\r" , "" , $texto );
$texto = preg_replace ( "/(http:\/\/[^(\)|[:space:])]*)\)/" ,
"<a href=\"\\1\" target=\"_blank\">\\1</a>)" ,
$texto );
$texto = preg_replace ( "/(http:\/\/[^([:space:]|\"|\<)]*)[[:space:]]/" ,
"<a href=\"\\1\" target=\"_blank\">\\1</a> " ,
$texto );
$texto = preg_replace ( "/\<a href=\"(.*zonasiete.*)\" target=\"_blank\"\>/" ,
"<a href=\"\\1\">" ,
$texto );
?>