to share files

dear sir,
i have one LAN.One win2000 advanced server and other client are WINxp. server has two network cards, external is 172.21.0.* and internal is 192.168.1.*. some clients are 172.21.0.* and other clients are 192.168.1.*. i want to see and copy files between these two networks. how can i do? pls, help me.
thanks for your help,