At first I thought you can go with downloading the driver and then doing modprobe driver_name (driver that need to be installed) then I realized you are working Backtrack 4 and am not sure if modprobe will work on that. And yes there is one more important thing that you shouldn't miss which is your kernel support for WiFi.
You have to check whether your kernel is configured for WiFi or not.
Have a look at the following link and you will understand what I am talking about
First check which kernel you are using by typing uname -a. Also check which architecture it is whether i386 or x86_64
Once done with the above step navigate to boot directory and see if you find any config files which says something like config-kernel_version (kernel_version will be output of uname -a)
Type the following command to read that file and see if it says something about WiFi under networking section:
Lets see how it goes. I have never worked on Backtrack 4 :-( but it worth giving a try to find out some information about kernel configuration related to WiFi.