Can a jumbo jet (like a 747) be landed purely on autopilot? A friend
of mine have suggested that you can land modern jumbo jets on
autopilot by "punching in the airport code, the Tower also tells the
type of landing you are doing - you enter that into the monitor." I
thought the notion was absurd. If anyone knows, please, shed some
light on this.

Yes, many types of commercial aircraft use automatic landing equipment
in order to make landings, and some carriers require that the autoland
feature is tested every so often. Here's a link to a discussion by
pilots about autolandings.

http://www.airliners.net/discussions/general_aviation/read.main/1882971/

Here is another article describing the autolanding systems, and
questioning whether or not full remote control capability is prudent.

http://www.public-action.com/911/facsnet/aviation.php3

Thank you for your question.

skermit-ga

Nelson DeMille's novel "The Lion's Game" uses an automatic landing as
a prominent plot device. According to DeMille (who is a pilot in
addition to being a writer):

"The newest generation of airliners can automatically control the
landing gear, flaps, and brakes, making a totally automatic landing a
routine operation. It's done every day. The computers, however, do not
control the reverse thrusters, so that an aircraft landing on
autopilot needs more runway than it normally would."

All modern Airbus aircraft, i believe, are fully automated from take
off to landing. If you've ever been on one and had a look in the
cockpit, the control is a tiny tiny joystick! I nearly had a fit when
i saw it! The airports have a beacon that lets the aircraft know its
exact position/velocity during take off/landing relative to the
runway. Hmm... I wonder if it'll be long before the captain is
something out of Airplane!.

Might be of interest:
http://seattlepi.nwsource.com/business/boe202.shtml

In an automated landing, the autopilot follows the glide slope down on
to  the runway and flairs automatically - providing it is setup
correctly. The spoilers and autobrake, if "armed," will also
deploy/activate too.

Being able to perform an automated landing depends on the equipment
available at the airport (the kind of approach system and its
accuracy) and on the aircraft (devices that lock the nose of the
aircraft onto the runway heading while slowing down on the runway) 
However, reverese thrust will not deploy, and nor can the aircraft
taxi to the gate. Flaps must also be set by the pilot manually on
approach.

Modern system's are accurate enough to be able to land the aircraft in
zero visibilty, however this is never used as the pilot would be
unable to find the gate after landing :)

Thanks for the input everyone, I didn't realize google answers is so great!

Your friend is perhaps oversimplifying autolands.  Yes, autolands can
be performed on modern aircraft and pilots are advised to try them
once in a few landings in good weather to keep current, so they'll be
comfortable when performing one in low visibility situations.  The
airport (specifically the runway), the airplane and the pilot all have
to be qualified before this should be done.  The ATC tower generally
is not involved.

The instrument landing system (ILS) for the runway sends out radio
beams for the airplane to follow to the landing.  Pilots usually set
an incercept course to "join" these radio beams (one for horizontal
and one for vertical) smoothly and the automation can take it from
there.   The "full autoland" is called Category III B autoland
capability.  With this capability, the airplane can land automatically
(flaps are manual only, like pointed out already) and rollout on the
runway down to about 40knots speed.  (Cat III C was only certified on
the Lockheed L1011 and has the capability to take you to the gate). 
As another reply says, the automation has the ability to land the
airplane at zero visibility (both horizontal and vertical), but this
is operationally not permitted as the airplane can't be taxiied (or in
case of a mishap, the emergency vehicles can't find the airplane).

Generally on a 747-400, three autopilot computers are doing the work
simultaneously and voting the result (in cruise flight, just one
autopilot normally flies the airplane) so even if one fails, it can be
isolated and the other two are fully capable of performing the
automatic landing.  In the flight testing of that autopilot, the
average error of of 100 landings was zero feet (with the standard
deviation of about 1.5 feet or so, if memory serves right).  It's been
a while since I worked on the design team. :)

I'm a retired airline pilot and a huge Nelson DeMille fan, but the
scenario presented in "Lion's Game" is absurd, for several reasons. 
True, as he writes, autoland will not activate reverse thrust on
landing, but there are other things it will not do--oh, minor items
like lowering the landing gear, extending the flaps, selecting
autobrakes, etc.  Plus, in preparing to use the autoland feature, the
pilot must first select the approach and runway to be used, after
listening to the ATIS and getting instructions from approach control,
and then "build" the approach in the FMC (flight management computer).
 No way would this be done two hours before landing, as he suggests. 
And, yes, sometimes autoland is mandatory (low ceiling and visibility,
assuming the aircraft, crew, and runway in use are CAT III certified).
 Or it could be "requested" (when the system needs to be tested every
number of cycles or days).  But 90 per cent of the time, pilots prefer
to hand-fly the aircraft for the approach and landing.  DeMille's
scenario has the bad guy killing everyone on board two hours prior,
then the aircraft landing itself--i.e., that the bad guy knew somehow
the autoland feature was hooked up and operating, a runway had been
selected, and so on.  He's a terrific writer, but the faulty set-up
for "Lion's Game" kinda ruined the book for me.