Well, you can generally achieve this without MetaTemplate. All you would need to do is ensure that there's a menu link to the VM component, then you would assign the desired template to that menu item in Joomla's Template Manager.
The advantage in MetaTemplate, if you want to use it, is that it does not require you to assign VM to a menu item. You can also be more specific about exactly which pages inside VM you want styled.
MetaTemplate Pro: just use the Components selector box on one of the rules, and choose VirtueMart from the box.
MetaTemplate: in the PHP box, use the following rule:
if ($option == "com_virtuemart") return true;
else return false;
For both the Pro and free version, you then do this:
- in the Actions section of the rule, use the drop-down to select the desired template for SUCCESS.
Hope that helps,
Stephen