[kh99]

There isn't much in the way of detailed documentation. You can look in the article section for somethign related to registration, but the best way (IMHO) is to look at register.php and see what's going on.

In your case, I think you could create a plugin using hook register_addmember_process and something like this:

if (!empty($vbulletin->GPC['userfield']['field5']))
{
    $url = 'http://www.xminecraft.net/haspaid.jsp?user=' . urlencode($vbulletin->GPC['userfield']['field5']);
    $reply = @file_get_contents($url);
    if ($reply === 'false')
    {
        // hasn't paid
        eval(standard_error(fetch_error('not_paid', $vbulletin->GPC['userfield']['field7'])));
    }
    else if ($reply !== 'true')
    {
        // couldn't complete check (site is down or whatever)
        eval(standard_error(fetch_error('check_failed')));
    }
}

and then you'd have to create the phrases 'not_paid' and 'check_failed' (you can chnage those varnames to whatever you want, of course).