No Luck Yet? Compile ndiswrapper from Source
You only need to do this if the Ubuntu ndiswrapper package doesn't work on your machine. For instance, Compaq F572US users report that after the above, NetworkManager doesn't show wireless networking, but report success after compiling and installing ndiswrapper from source.
For Gutsy and Hardy users, it's pretty unlikely that you need to compile ndiswrapper, as this package is reasonably up-to-date in those releases.
Remove Stock ndiswrapper
sudo modprobe -r ndiswrapper
sudo ndiswrapper -r bcmwl5
sudo apt-get remove ndiswrapper-utils
sudo rm -r /etc/ndiswrapper/
sudo rm -r /etc/modprobe.d/ndiswrapper
Now, REBOOT.
Compile and Install New ndiswrapper
Feb 04, 2010: Instructions now point to ndiswrapper version 1.55
sudo apt-get update
sudo apt-get install build-essential
sudo apt-get install linux-headers-`uname -r`
sudo ln -s /usr/src/linux-`uname -r` /lib/modules/`uname -r`/build
mkdir -p ~/bcm43xx/ndiswrapper; cd ~/bcm43xx/ndiswrapper
sudo wget http://downloads.sourceforge.net/ndiswrapper/ndiswrapper-1.55.tar.gz -Ondiswrapper.tar.gz
tar xvzf ndiswrapper.tar.gz
cd ndiswrapper*
make distclean
make
sudo make install
Redo Some Steps That Were Undone by ndiswrapper Compilation/Installation
cd ~/bcm43xx
sudo ndiswrapper -i bcmwl5.inf
ndiswrapper -l
sudo modprobe ndiswrapper
sudo ndiswrapper -m
Now, REBOOT.