first, run iwconfig, and see if wlan0 (or wifi0) is listed. if not, carry on with lspci, etc. below.
run lspci, and do a google and forum search for your wireless card's compatibility with backtrack 4 final, or linux. if you *still* can't find it, let us know by running lspci and posting the results for your wireless card... and chances are that we'll find it, or something useful for you.