[consolegaming]

Well if you want a very easy way you could use the following plugin:

https://vborg.vbsupport.ru/showthread.php?t=108026

This involves basically including parts of vB on your site (nothing visible but it auto fills some arrays, checks you're logged in etc). There are a few drawbacks to this though which is why we're not using it, if the forum is closed or if a user is temp suspended it seems this same block that stops the user from accessing the forum is also in place for the site too. At our site at least we don't want people not to able to view the site just because they spammed on the forums lol.

If those are disadvantages you can't put up with then the following may well help you:

What we did was use the forum's login script i.e. passed our login info to the login.php page and then on our own site header check for the existence of the cookies vb creates.

For the first part (passing the login info we simply looked at what the forum's login box usually passed to login.php and duplicated it.

and for checking if they were logged in we just did something like;

if (isset($_COOKIE['bbuserid']))
{
$userid = $_COOKIE['bbuserid'];
$userinfo = mysql_fetch_array(mysql_query("SELECT * FROM user WHERE userid = '$userid'"));
}

Also for my suggestion or the above plugin to work on multiple subdomains i.e. if you have forum.website.com or other subdomains you need to alter the value in the forum's admincp at: vBulletin Options -> Cookie and HTTP Header Options -> Cookie DOmain -> Custom Domain then do the following:

if you're website is http:www.google.com then you'd chaneg the cookie domain to .google.com
i.e. a dot then just the main domain.

Hope that helps at least a bit.