You will normally not want to use regular hypertext links in MiniVend pages. Such links will not include the session id, which means that if the customer follows an external link back to the catalog the list of products ordered so far will have been lost.
So instead of:
<A HREF="/cgi-bin/mv/shirts">Shirts</A>
You would use:
<A HREF="[area shirts]">Shirts</A>