[davidw]

You'll need to do these things:
1) Create your template, templatename, which you've already done and
2) Create 2 plugins
Go to your admincp => Plugins & Products => Add New Plugin =>

Plugin 1
Product - vbulletin
Hook Location - cache_templates
Title - Title of Plugin 1
Plugin PHP Code -

$globaltemplates[] = 'templatename';

and

Plugin 2
Product - vbulletin
Hook Location - global_start
Title - Title of Plugin 2
Plugin PHP Code

global $db, $vbulletin;
eval('$templatename .= "' . fetch_template('templatename') . '";');