Cisco is a massive company that offers a broad selection of hardware products, software, and services.
As friedo mentioned, their primary product line is routers and switches. Pretty much anything relating to moving bits around on a network. When I worked there, they had more people writing software than they did designing hardware, but most of the software was for their own proprietary products.
As for the second question, they company was at the core of the dot-com boom because most dot-com companies used (and still use) Cisco products at the cores of their networks.