I'm using PHP 4.3.0
I found problem when using preg_replace(..)
string $0 and $1 will mess up and not replace correctly
also $N with N is Integer will not appear. If the character after the dollar sign is not a number, it works as expected.

Here is my code:
<?php
/*** PHP START***/
// Found: 26-03-2003

$strBuffer=
'
<pre>
----------------------
preg_replace() bug???
----------------------
<LOOP>
[NUMBER]         [MESG]
</LOOP>
----------------------
</pre>
';
$strNumber = 123456789;
$strMesg   = "text with $0 and $1 string";

$Patttern = "/<LOOP>(.*?)<\/LOOP>/is";
preg_match($Patttern, $strBuffer, $arrTag);
$strData  = str_replace("[NUMBER]",   $strNumber, $arrTag[1]);
$strData  = str_replace("[MESG]",     $strMesg,   $strData);
$strBuffer= preg_replace($Patttern, $strData, $strBuffer);
echo $strBuffer;

/*** PHP END***/
?>