In 12.04, and in 11.10 and 11.04, simply clicking on the .deb file should open the package manager, where you just press the "install" button. but if you want to use the terminal, more power to you. I would the the cupswrapper.deb file. download it, and keep in mind where its saved. for this example, I saved it in my Downloads folder.
according to Brother, you have 1 dependencies, lets install them first in terminal:
sudo apt-get install ia32-libs
it might already be installed, but its good to check.
now to the .deb file. navigate to where you saved the file in your terminal. for me, thats my download folder:
do and "ls" to verify you see the .deb
sudo dpkg -i cupswrapper.deb
and follow the onscreen instructions, if any.
I dont know how long it will take to run the deb. I know HP drivers took about 10 minutes on my system, but it was a much larger file.