A lot depends on which computer has the physical connection. WinNT does not come with the capability of sharing a connection, but Win98 does. If your Win98 machine has the connection, install and configure Internet Connection Sharing (ICS) on thatmachine. Any PC on your LAN will be able to access the Internet through that connection.
If the WinNT machine has the connection, install a free proxy, such as AnalogX, to share it. You'll need to configure the other PC to use a proxy server,and set the port to 6588, rather than the default port 80.
By the way, Routing and Remote Access (RRAS) should allow this, but in four years of trying I've never found a way to do so. There is plenty of documentation, but all of it is meaningless babble. After years of trying to decipher the cryptic bull in the Microsoft docs, I installed Proxy Server 2.0 and managed to get everyone connected. With a Win98 PC available, though, you should be able to avoid that cost. ICS makes it fairly easy.