[AlokSharma]

Just in case, if someone only wants to add a tab, here is the modified code:

PHP Code:

$tabselected = '';
$tablinks = '';
if (THIS_SCRIPT == 'chat')
{
    $vbulletin->options['selectednavtab']='chat';
    $tabselected = ' class="selected"';
} 
$template_hook['navtab_end'] .= '<li'.$tabselected.'><a class="navtab" href="chat.php">Chat</a>'.$tablinks.'</li>' ; 


Replace:

PHP Code:

if (THIS_SCRIPT == 'chat') 


and

PHP Code:

$vbulletin->options['selectednavtab']='chat'; 


With some unique name.