After choosing their vehicle from the homepage, product from all categories can be displayed in a variety of formats
Product results from all categories can be displayed in a standard Magento grid or list view.
A break down of categories with images can be displayed, which would show only categories that have product matching the vehicle searched on.
This allows users to expand and collapse categories, similiar to how "folders" on your computer work.
The vehicle the user is searching on is clearly displayed at the top of the page.