I bought the Alfa awus050nh usb wireless adapter a couple of days ago and after extensive searching on this site and google, I eventually used the following tutorial to get it working with injection in BT4F.
NOTE: Ralink RT2870_Firmware is now v22 not v8 as in the tutorialCode:http://sudonetworks.com/wiki/index.php?title=ALFA_AWUS050NH_Driver_Update_for_BT4
It seems to be working well. I hope this helps others who are/were in the same boat.
Cheers to the tut author and all the little contributing posters on the many threads I read.