[winstone]

create a plugin with following code:

PHP Code:

vB_Template::preRegister( 
    'SHOWTHREAD', array('forumTitle' => $forumTitle) 
); 


Product: vBulletin
Hook Location: showthread_complete

save and activate the plugin
in SHOWTHREAD template, find

<title>{vb:raw thread.prefix_plain_html} {vb:raw thread.title}</title>

replace with

<title>{vb:raw thread.prefix_plain_html} {vb:raw thread.title} - {vb:raw forumTitle}</title>