brother mfc7420 to print under ubuntu 12.04

You need to down load both the lpr and Cups drivers, you want the deb files,then install as follows
replacing <lpr-driver.deb> and <cups-driver.deb> with the actual names of the files

Step 1. Download drivers
   You have done that already
   Open a terminal and move to that directory

Step 2
   You need to have a directory called "/var/spool/lpd" if you don't create it with
   sudo mkdir /var/spool/lpd

Step 3. Install LPR driver and cupswrapper driver
    3-1. Turn on the printer and connect the USB cable if connecting via USB, No need to connect in using LAN.
    3-2. Open the terminal and go to the directory where the drivers are.
    3-3. Install LPR driver.The install process may take some time. Please wait until it is complete.

        Command:
        sudo dpkg -i --force-all <lpr-driver.deb>

    3-4. Install cupswrapper driver.The install process may take some time. Please wait until it is complete.

        Command :
        sudo dpkg -i --force-all <cups-driver.deb>

    3-5. Check if the LPR driver and cupswrapper driver are installed

        Command:
        dpkg -l | grep Brother

Step 4a. (for USB Connection) Check your printer on the cups web interface
    4a-1. Open a web browser and go to "http://localhost:631/printers".

        Check if the Device URI of your printer is "usb://Brother/(your printer's model name)"
        Example of a USB printer entry
        If the device URI is different from the example above, please go to "Modify Printer" of your printer to select proper device and driver.

        If your printer is not listed on "http://localhost:631/printers", please go to "http://localhost:631/admin" and click "Add printer" and select proper device and driver.

Step 4b. (for Network Connection) Configure your printer on the cups web interface
    Its easier if you give your printer a fixed IP
    4b-1. Open a web browser and go to "http://localhost:631/printers".
    4b-2. Click "Modify Printer" and set following parameters.

    - "LPD/LPR Host or Printer" or "AppSocket/HP JetDirect" for Device
    - lpd://(Your printer's IP address)/binary_p1 for Device URI
    - Brother for Make/Manufacturer Selection
    - Your printer's name for Model/Driver Selection
        Example of a network printer entry

Step 5. Try a test print
    5-1. Open a text editor, write something and select "print" from the menu.

Step 6 delete the drivers you have downloaded don't need anymore

Thanks a lot Warren! I've followed your instructions and my mfc-7420 works