VirtueMart was written to be used inside a Content Management System (CMS) called Joomla! (also: Mambo).
All you need is to download the latest Joomla! eCommerce Edition from this site.
You can now use a shop component within your own "portal" together with much other components and modules like forums, faq, guestbooks, galleries and so on, which are available for Joomla! (mostly for free). Even if you think that you don't need such a portal and a big CMS - you are more flexible with it. Change the look and feel of your site by using the Mambo Templates, which use CSS and X/HTML.