Creating a Login Script

[10sion]

Alright im trying to create a login script for the forum, dont ask me why but I need to create another one that logs the user in the forums, one thing got me stuck though, vbulletin encrypts the passwords and I cant figure out there encryption method.

All I need to do is compare the posted password (then encrypt it and i dont know how) to the password in the database, anyone care to show me how to encrypt it, NOTE: I cannot include any of the vbulletin files in my code.

Heres what you have to work off of:

<?php
$username = $_POST['username'];
$password = $_POST['password'];
?>

I know the password is not just md5'ed i saw something like utf, never heard of it, and theres a salt stored in the database for each user, dont know what its for... please help its really important .