Needed to bring up a small broadcom based usb dongle that wasn't immediately recognized by my Porteus 4.0 X86_64 XFCE. It was from an old RPI project.
In the archives, this EASY great thread was brought up by fanthom:
[HOWTO] Broadcom wifi under Porteus
The steps were pretty simple, although for some reason, it seemed I needed to name the blacklist file b43_blacklist.conf, and not the generic broadcom_blacklist.conf. Looks like that may not make a difference, but on my box using about 15 cheatcodes, it did.

To reiterate what fanthom said -if the standard broadcom sta driver does not recognize your card, blacklist it and try this:
1) As root, create this directory structure:
/mnt/sdXY/porteus/rootcopy/etc/modprobe.d <<-note your sdxy boot device may be different
Since I hadn't done anything with rootcopy, I needed to manually create directories for etc and modprobe.d (mkdir ....)
Inside the modprobe.d directory, edit a new file:
b43_blacklist.conf
And inside that file the contents simply consist of this one line:
blacklist wl
2) Save file, and reboot
Right on - works like a champ. For this card at least.