IP addresses for internal networks usually start at 192.168.0.1, x.x.x.2, x.x.x.3, and so on. The gateway is only needed on the computer that connects to the internet if you plan to use wingate, sygate, ICS, etc.

Since you have w2k, the best way to share an internet connection is ICS, it really works great. Just set both computers to use dynamic IP addresses and then on the one with the internet connection click the sharing tab and the select the "share this connection" box. That's all.