First you have to know that your wifi card is recognized and network service is running .once it is done you can check your card. If you had dual book installation, Network Service starts automatically.
Starting network services:
Then try this one.
xxx@bt>/etc/init.d/networking start (if you use Networking Manager, wich is not used in BT5)
xxx@bt>/etc/init.d/wicd start (if you use Networking Manager, used by BT5)
xxx@bt>lspci | grep Network (Internal wifi card, pci) (lspci means to "LS list PCI pci = lspci)
xxx@bt>lsusb (list all USB) Look up if you see your usb wifi card..
You can also check the driver and see if it has been loaded:
xxx@bt>lsmod | grep ieee80211 (if it uses ieee80211 stack) But trt this option first
xxx@bt>lsmod | grep mac80211 (if it uses mac80211 stack)
Atleast this way u you can verify whats going inside your card. If interface or module is not present than your wifi card is not supported. Try to figure out what is going on just try above commands. Backtrack 5 is based in debian with kernel 2.6.xx .you can find all troubleshooting from aircrack 墨g website. With backtrack 5 u can do two things in aircrack: Place the wifi card in Monitor Mode and being able to inject traffic. If driver is not fixed, you will not be able to make use of the suite as planned. Also in the aircrack page you can download the Patch and apply it to you wifi card, and compile it physically with the kernel, as extended as wifi card is supported. This is the benefit Backtrack 5 give you in the middle of others, drivers patched to use them with the aircrack suite. You saved lot of time and I hope above solution helps you out.