Just in case you guys are interested.
I've given up trying to modify the internals of the Android tablet to directly connect the Arduino.
This is because it looks like all USB hubs (and the one I was testing) don't work on 3.3V. So I'd need a separate 5V supply for this.
And it wouldn't be running on the same voltage as the tablet and would drain the battery a lot if I fitted a 3.3V to 5V up-converter.
So as my cheapo tablet doesn't have BlueTooth (none of the cheap ones I've looked at online see to have BlueTooth, it seems to be something that limited to more expensive models), I'm going to use an external Wifi based solution.
i.e connect a "Uart Wifi" module to my Arduino and then change the wifi settings in the tablet to use the Arduino's wifi as if it was a base station (Access Point).
This means I won't have to risk damaging the tablet.
The downside is I'll keep needing to change the wifi settings every time I want to communicate with the Arduino, but for development purposes, I will probably change the "Uart Wifi" module to operate as another client (Station), and put it on a fixed IP, so I don't have issues with the Android software accessing it.
So all I need to do now is learn how to program Android in Java ;-)
(Actually you can do it using Flash - via Adobe Air, which would make for nicer looking UI's ;-)