Some (but not all) Broadcom 43xx Wireless cards (primarily newer cards) do not have the necessary firmware readily available in order to use the b43 driver module. However, as pointed out in a forum post by Juanito, using the 32-bit kernel and the bootcodes “blacklist=b43 blacklist=bcma blacklist=ssb” allows the wl driver module to be loaded. After booting with these bootcodes, either from the virtual terminal or from your preferred terminal emulator (like aterm), do

sudo modprobe wl

to load the wl driver module. At this point, the wireless utility (present by default in MultiCore) will detect the card appropriately.