There is  many ways to create a custom menu for virtuemart categories. The most popular style of menu for virtuemart is showing all parent categories in a menu and the child categories will be listed in the main content area when the parent one is clicked.

You also can make a module to show the virtuemart categories in a vertical menu on left and when a category is clicked, the menu opens to show all products in that category. Once the product in the menu is clicked, it should go directly to the full 'Product details' page.

The example site with this type of menu is http://www.raoul.ca/heron. With this module, you can choose which category and its products will be listed in a vertical menu or all categories.