You can do it by setting you regulatory file to another region (which I won't tell you since it's easy to find both on google and those forums).
You do not have to install anything on Backtrack, driver rtl8187 does a great job (assuming AWUS036H).
I didn't hear anything about two cables and I got it working to 1W with only one. From memory, USB can handle 1W without any problem.
To find out if your card is working at max capacities, check its txpower
I hope this points you in the right direction for searches!