Assume there is USB network connection and a LAN Ethernet connection on the same XP box.
The USB connection is set up as the Internet Connection Sharing (ICS) connection.
The following describes setting up a bridge between the USB connection and the NIC on the XP box.
This is best described in the article USB Network Bridge and more espically by the link part way down the page with the "Windows XP Network Bridge" link Win XP Bridge. At the section beginning "Windows XP offers another, much better possibility : to create a "Network Bridge" there are screen shots taking you through how to use the USB connection over the Ethernet NIC to the LAN (hub).