The easiest way... if you don't wish to turn on new user approval... is to override the email that would normally get sent for users that need approval. This won't turn on the approval process... it'll just send the email to the admin anyway.
In adduser.php find this.... and remove (or comment out) the lines in Red.

code:
// ---------------------------------------------------------------------
// Now if we are manually approving user registration we need to send an
// email to all admins
[:"red"] if ($config['userreg']) {[/]
$query = "
SELECT U_Email
FROM {$config['tbprefix']}Users
WHERE U_Status = 'Administrator'
";
$sth = $dbh -> do_query($query);
while(list($adminemail) = $dbh -> fetch_array($sth)) {
if (!$adminemail) {
continue;
}
$newuser = rawurlencode($Username);
$to = $adminemail;
$header = $mailer -> headers();
$subject = "{$ubbt_lang['NEWREG']} {$config['title']}";
$msg = "{$ubbt_lang['NEWREGBODY']} {$config['phpurl']}/admin....
mail("$to","$subject","$msg",$header);
}
[:"red"] }[/]
Edit: Careful not to miss removing that last } if you remove the if. the color is tough to see on the } by itself.

I also shorteded the one line with the URL so that Dave_L doesn't have to scroll.

Hope that works for ya.
