No need to patch your drivers with bt4 ... and if your not on bt4 then you should be.
I have an Alfa 500Mw AWUS036H usb and followed a guide on the Aircrack site and patched my drivers but when I run an injection test (aireplay-ng -9 wlan1) and get the following:
13:23:06 Trying broadcast probe requests...
13:23:08 No Answer...
13:23:08 Found 1 AP
13:23:08 Trying directed probe requests...
13:23:08 <ADR:ES:SS> - channel: 10 - 'BTVOYAGER2091-6C'
13:23:14 0/30: 0%
No need to patch your drivers with bt4 ... and if your not on bt4 then you should be.
Using backtrack for the first time is like being 10 years old again with the keys to a Ferrari.