I picked up a new machine this week to turn into a home media server, and had a small hoop to jump through with the Broadcom wifi card I picked up. Problem being, office and all my monitors were upstairs, wifi was downstairs, and it's difficult to install new drivers without net access.
But, Linux Mint popped up a "new hardware" dialog, saying it wanted to use b43-fwripper to set up the drivers. Good news, it gave me the url it failed to download from. Manually download the deb, open it up on my other machine using Archive Manager (rather than GDebi), and navigate through to the postinstall script, at data.tar.gz/./usr/share/b43-fwcutter/, and I find a reference to two other files.
After downloading those, copy all three files to the new box. Copy the .deb to /var/cache/apt/archives, and then apt-get install b43-fwripper. Ignore the failure, then go to the dir with the other two files, and manually run the 3 useful lines from the install script (don't forget to add sudo to the last one):
b43-fwcutter -w /lib/firmware wl_apsta-18.104.22.168.o tar xfvj broadcom-wl-22.214.171.124.tar.bz2 b43-fwcutter --unsupported -w /lib/firmware broadcom-wl-126.96.36.199/driver/wl_apsta_mimo.o
Reboot, and voila - local wifi networks show up in the tray applet. I presume these steps will work for an Ubuntu install as well, since Mint is based on Ubuntu, but I haven't tried it as yet - in fact, the required .deb is on the Ubuntu 9.04 livecd. I also don't know if these files will work for other Broadcom wireless adapters, but if your modern linux system can do a hardware detect and tell you what driver it's trying to pull down, that should be a good starting point.