[kh99]

You shouldn't use 's' as your parameter. s is already used in the vbulletin code for something else. I'll use 'x' in the example, but you can change it if you want (probably best to avoid single letters so it doesn't conflict with anything else).

You would need to create a plugin using hook newthread_start and code like this:

$vbulletin->input->clean_gpc('g', 'x', TYPE_INT);
$x = $vbulletin->GPC['x'];
// you could add code here to check for valid values of $x
if ($x == 3)
{
    // change below to redirect url - if it is an external url, you must add it
    // to the redirect whitelist in the options in the admimCP
    $vbulletin->url = "http://redirect_url"; 
    standard_redirect();
}
vB_Template::preRegister('newthread', array('x' => $x));

then in the newthread template, something like:

<vb:if condition="$x == 1">abc</vb:if>
<vb:if condition="$x == 2">fgh</vb:if>