An alternate that won't require you to edit any templates, and will work in all of your styles would be to create the following plugin:
Product: vBulletin
Hook Location: parse_templates
Title: Add Text Before Breadcrumb
Execution Order: 5
PHP Plugin Code:
PHP Code:
$vbulletin->templatecache['navbar'] = str_replace('<li class="navbithome">', '<li class="navbithome"><span>You are at: </span>', $vbulletin->templatecache['navbar']);
Plugin is Active: Yes
Click "Save".