So you don't have the Windows 2000 Server on an Internet facing adapter (at least not as your first server in line) and you have your router or gateway block Ports 139 and 445 from the Internet.

Then, you only have to worry about intranet related threats. Although with the ports blocked on the gateway, you shouldn't have an issue with that (unless there's malware created which uses a click to install from a website).

Have a great day
Patrick.