Microsoft Knowledge Base Article 307311 contains the following summary:

Internet Connection Sharing (ICS) enables you to use Windows 2000 Professional to connect a small office network or home network with the Internet. ICS provides network address translation (NAT), IP addressing, and name resolution services for all the computers on a small network. This step-by-step article describes how to install ICS on Windows 2000 Professional operating systems.

The following hardware or software is required for this procedure:

• DSL or cable modem connected to an Internet Service Provider (ISP) and an activated DSL or cable account.

• Two installed network adapters. This article describes how to install a second network adapter.

• The network is already configured with functioning TCP/IP.