useful link:
http://linuxwireless.org/en/users/Drivers/b43#devicefirmware # in latest versions of Ubuntu (all flavors) and Debian just need to install the b43-fwcutter package:
sudo apt-get install b43-fwcutter
when you are asked "Fetch and install firmware?" answer "Yes" (just press "Enter)
BTW
# openSUSE 11.0 and 11.1 use the following command:
sudo /usr/sbin/install_bcm43xx_firmware