I'm not sure I understand the question. If you're asking if a Windows 2000 server can be used by an ISP for dial-in clients, the answer is yes. It can be done with RRAS and a specialized piece of hardware. However, that's rarely a cost-effective technique. Generally, considering all ISPs have to handle, you'll be better off purchasing a hardware solution designed for the purpose.
This was first published in July 2003