Prolific manufacture a range of USB chips, including the PL2301 and PL2302 devices that allow two USB host controllers to be linked, providing a simple point to point link at up to 5Mbps. This driver supports both PL2301 andPL2302 chips.
Aserton, Bencent, Butterfly, Camtel, Longshine, Prolific, StarMount, Swann, Univex and VVMer cables are all known to use the PL2301 or PL2302 chips. Entrega, Xircom and Belkin adapters do not use Prolific chips and are not supported by this driver.
In addition to selecting this option to either be compiled into the kernel or to be build as a module, you need to configure the appropriate networking interfaces. If you have two machines (say zhora and rachel, then on zhora you would enter ifconfig plusb0 192.168.0.1 pointopoint 192.168.0.2. On rachel you would enter ifconfig plusb0 192.168.0.2 pointopoint 192.168.0.1. To test that it is working, on zhora, enter ping 192.168.0.2. If you get packets back, it is working correctly.
For further information on networking, I suggest that you refer to the many excellent Linux networking documents, including the Linux Network Administrators' Guide and the Linux Network HOWTO.