Sure - this is pretty easy.
You have to change what's called the "Metric" in Windows. The metric, when set to a lower number, is the priority of the connection. When disconnected, the metric turns 'off'. Now if you're running Windows 7 Ultimate, it SHOULD automatically use an Ethernet connection but because it's a USB device, it might be losing priority.
If you're using a tablet, why don't you just hit the "wifi off" button or there isn't one?
About changing the metric:
Go into your windows control panel, and look for the Network places/Networks and Connections.
In the top left, you should see "Advanced settings" or something like that (I'm at work, we have WinXP so I'm doing this from memory)
In your advanced settings you might see a few different network adapters. We need to set the metric for these adapters telling windows to use one over another.
Right click on the wireless adapter, select Properties.
Look for something that says "TCP/IP v4" and select it. Click the properties button in that panel.
The new one that comes up should have DNS and DHCP settings on it somewhere with "Advanced" in the bottom right. Click Advanced.
See at the bottom of the IP Tab? You should see something checkmarked that says "Automatic Metric"
Change that so it's unchecked and you can put a number in the box. Put in 10 here.
Now go back to the USB ethernet and do the exact same thing, but make the number less than 10.
That way, when Windows has an Ethernet connection it will "prefer" this connection. Alternatively if it's not available it will use the wireless connection
Hopefully my steps are right, but if not, I'll update when I get home from Work in around 6 hours.
