I have exactly the same problem, and it was resolved in (almost) the same way.
After running installer, machine rebooted. Ubuntu splashscreen appeared and the blue bar froze a fraction of the way along. Then, after waiting for some time, the BusyBox error appeared.
I disabled the nic built into my M848A motherboard, installed a pci nic, reran the installer, and got to the a/v setup page.