So they are networked properly? I believe you find that option in the dial up connection properties. There should be that option to share the connection that Oni mentioned before. Maybe this might help:
The ICS host computer provides a connection through the second network adapter to the existing TCP/IP network. Log on as member of the Administrators group to set up the ICS host computer.
Click Start, click Settings, and then click Network and Dial-up Connections.
Right-click Local Area Connection (the network card that you just installed), and then rename it "The Internet Connection".
In the Network and Dial-up Connections dialog box, two connections are displayed (for different network adapters), The Internet Connection and Local Area Connection.
Right-click The Internet Connection and click Properties.
Click the General tab, and then verify that Client for Microsoft Networks and Internet Protocol (TCP/IP) are displayed.
Click the Sharing tab, and then click to select the Enable Internet Connection Sharing for this Connection check box.
NOTE: Make sure that firewall software or other Internet sharing software from a third-party manufacturer has been removed.
Click OK and exit to the desktop.