[<?Wille?>]

something like this?

PHP Code:

$ip = '82.181.38.134';

$msg = preg_replace("#((25[0-5]|2[0-4][0-9]|[0-1]{1}[0-9]{2}|[1-9]{1}[0-9]{1}|[1-9])\.(25[0-5]|2[0-4][0-9]|[0-1]{1}[0-9]{2}|[1-9]{1}[0-9]{1}|[1-9]|0)\.(25[0-5]|2[0-4][0-9]|[0-1]{1}[0-9]{2}|[1-9]{1}[0-9]{1}|[1-9]|0)\.(25[0-5]|2[0-4][0-9]|[0-1]{1}[0-9]{2}|[1-9]{1}[0-9]{1}|[0-9]))#sie", "stripslashes('\<a href=\"page.php?\\1\"\>\\1\</a\>')", $ip);

echo $msg; 

and btw.. the part matching the ip MUST be one long line..
and also i would like to point out that your code also accepts 999.999.999.999 witch is a invalid ip.
hope it helps