You can, in theory, plug an external wifi dongle into the chumby and have it work, as long as it is an RT2571-based chipset dongle.

The problem is that the RT73 kernel module panics when it sees two RT2571's plugged in.

One way around this is to disable the internal USB port by configuring the pins on the MX21 to be GPIOs instead of as USB signals. That way the chumby will only see the external dongle that you've put in.

You have to do this right away at startup--unfortunately, you can't do this with a loadable kernel module, because the USB enumerates before any modules are loaded; you have to do this by hacking the kernel itself and reflashing it. I spent a couple hours banging my head on this one before I figured it out. Even if the driver for the RT73.ko isn't loaded in, USB is enumerated and the descriptor for the device is hanging out in the USB driver. What happens when you turn off the USB port and then try to load the module is that instead of associating the driver with the wireless card plugged into the back, the kernel tries really hard to mount a now phantom device on the internal port and eventually dies a flaming death.

However, really the right thing to do would be to figure out why the RT73 module panics when you have two NICs plugged in--this shouldn't be a problem for the driver, I think, if it is well written.