Installing the printer drivers:
1) Change directory to the folder containing the drivers.
2) mkdir /usr/share/cups/model
3) dpkg -i --force-all --force-architecture (lpr-drivername)
4) dpkg -i --force-all --force-architecture (cupswrapper-drivername)
5) Check if the drivers installed: dpkg -l | grep Brother
   
Installing the scanner drivers:
6) If you don't have sane-utils, install it: apt-get install sane-utils
7) dpkg -i --force-all (scanner-drivername)
8) dpkg -i --force-all (scan-key-toolname)
9) Check if the drivers installed: dpkg -l | grep Brother

Provide consistent naming for your scanner device:
10) Open "/lib/udev/rules.d/60-libsane.rules" file with you favorite editor, and add the following two lines to the end of the device list,
(Before the line "# The following rule will disable ..."):

# Brother scanners
ATTRS{idVendor}=="04f9", ENV{libsane_matched}="yes"

11) Restart

The above procedure would work for both printer and scanner. However, since I have moved to xfce4, I have not yet been able to set up my scanner. The printer works fine, but the scanner doesn't. This is the message that I get from my scanner (Simple Scanner): couldn't connect to scanner.

Also, based on the recommendation from http://www.reactivated.net/writing_udev_rules.html I tried a different location for the udev file ( /etc/udev/rules.d/), but that didn't solve the problem either.

One strange thing that I noted (during choosing the model for my printer in the CUPS interface) there were two identical model names in the Model list:
Brother DCP7040 for CUPS (en)
Brother DCP7040 for CUPS (en)

I suppose with xfce4, there must be a new approach with managing udev files. Or maybe the problem is not with managing udev this time? Anyone has any suggestion?