Open a Terminal and type in:
Find your Internal card there and comment it out using a # sign
Make sure you disconnect your AWUS036H so you don't disable it by mistake.
When your done Press CTRL + X and then press y for yes and then press enter should take you back to the root@bt:~#
Next type in the Terminal: /etc/init.d/networking restart
Now do a iwconfig and see if your internal card is listed if its not its disabled now plug your AWUS036H in and that should be your default card.