The jailbreak simply allows stuff to be run.
Then one installs usbnetworking from the right thread
From there:
In a nutshell: The USB on the PC end needs an IP assigning to it.
This must match what is in the usbnet config in [/mnt/us/]usbnet/etc/config
being on a different subnet (192.168.x.blah) to your main LAN doesn't matter.
however the subnet of the PC (USB) IP and the Kindle must match.
192.168.blah.1 192.168.blah.2
or 192.168.yaddayadda.1 192.168.yaddayadda.2
(192.168.15.201 and 192.168.15.1 would be a "real world" example)
If you use windows it can be a bumpain to do the initial config on the PC but once it is done you should be golden.
EDIT: Don't mistake your main LAN's IP address as your PC side IP address for the USBNET connection... It isn't - to reiterate... you need to assign an IP to your USB0 connection...
Good luck.
Here is another way:
(Hint: SSH works just as good over Wifi.)
connect to wifi on kindle.
enable usbnet.
go to 411? or 711? page (IP INFO PAGE) find ip... (Typically 192.168.1.low-number)
on PC: (for windows use putty) on linux ssh
root@192.168.1.the-low-number
you will need to press enter when prompted for pw (will be blank)
that should be easiest. Both ways (usb or Wifi) should work just fine
(That is a mail I sent recently)
Hope that helps somewhat.