Bridging to Autcion site

[Rented]

Hi,
I have a forum and an auction site.
Literally the users sign up at the vBulletin forum and they are automatically signed up to the Auction site.
Here is part of the auction site login script.:

PHP Code:

if (isset($_POST['loginok'])||$_POST['islogin']=="yes") {
$userDetails = getSqlRow("SELECT * FROM probid_users WHERE username='".$_POST['username']."'");
$salt = getSqlRow("SELECT salt FROM probid_users WHERE username='".$_POST['username']."'");
if ($setts['account_mode_personal']==1) {
$account_mode_local = ($userDetails['payment_mode']==1) ? 2 : 1;
} else $account_mode_local = $setts['account_mode'];
if (substr($userDetails['password'],0,10)==substr(md5(md5($_POST['password']) . $salt),0,10)&&$_POST['password']!=""&&$_POST['username']!="") { 


I can't however login in. It says incorrrect password. I have check all the data is in the table, including salt.
However I don't know if I have done this bit right:

PHP Code:

substr(md5(md5($_POST['password']) . $salt) 


I was told it should be like this:

PHP Code:

$password_hash = md5(md5($password_text) . $user_salt); 


I have a cron job to copy all the user information including the salt data, so all the data is there.

What am I doing wrong though?
Thanks