Sharing internet over USB-- how hard?

[C(-)ris]

microchip wrote:
...I don't understand why Ethernet won't work just fine?

Because there is no way to share an internet connection from a USB connected modem. Modem has 1 ethernet port, iMac and MDD also each only have 1 ethernet port. To use ethernet, at least one of the devices needs to have 2 ethernet ports.