how to share file without sharing LAN?

We would like to access files from a stand-alone CAD workstation (XP Pro) without joining it on to the LAN domain (TCP/IP). The machine already has a NIC for broadband connection. Can this be achieved by adding a second NIC with a seperate set of IP address that the LAN would recognize? We also do not want inbound traffic from the CAD machine getting into the LAN.

Any suggestion would greatly be appreciated.