Please provide more info on the hardware (dsl modem, router, and NICs). We could also use more info on the actual setup.
DSL modem connected to internet.
Router connected to DSL modem via network cable.
PC#1 is connected to router via network cable.
PC#2 is connected to what through USB port? Is it a USB NIC? This is where I'm lost.
Also, please post the output of lsmod