The only difference is how long your license key is valid for. However your users can be using Macintosh computers or Novell server attached computers. Some web servers can be configured to host more than one web site or unique domains. These web sites are called virtual hosts and share a single IP address. That means that each of these virtual hosts resolves via DNS to the same IP address.
Virtual hosts require special categorization in order to be properly identified and screened.
Otherwise, the system would lump sites that had no commonality into one over broad category. The license levels are thus not a simultaneous use license, but a total number of machines license. We recommend that you use IIS version 3.0. After installation, MS Proxy Server MUST be restarted.