I would like to connect two LANs from one PC. The first network will be used for application software and the second for Internet and e-mail. The application network is owned by another company and ...

Ethernet ports are usually just relegated to connecting computers to routers to facilitate an internet connection, but they're capable of much more than that.

You don't need a router. If you set the subnet mask on all of the PCs to be 255.255.0.0, then they should all be able to ping each other. Basically, opening up the subnet mask puts all of the PCs on ...