actuallly even if you do have a net connection that assigns your Internet connected NIC an IP in the 192.168.1.x range, , you can always use fixed IPs on a different range for your LAN...
I am also facing this problem I connect my laptop to my desktop by a RJ45 cable I want to set up a connection by winxp home or office network but the connection fails........I also tried to set up an wireless connection with my friend's laptop but I face similar problem there