You can't use a PCI wireless card with backtrack running on VM, Backtrack will view it as an ethernet card so you need to use a USB wireless NIC.
To enable the USB wireless with VM, when backtrack is powered up, go to VM > Removable devices > to your wireless > connect.
I use the Edimax USB device with my backtrack VM and it works like a treat!! Crack WEP easily done.



