I read an article today that said that high definition DVDs were on their way,
and that anyone who has ever tried to view an existing DVD on their HD TV were
no doubt disappointed with the resolution.

As a rule, I do NOT watch DVDs. Instead, I watch cable TV.
So, the article got me to thinking about all the 'stages'
that a signal must go through before it reaches my television set.

For example, I can think of 5 'stages' that a program must go through:
(1) Original programming has to be created and stored for later viewing.
(2) A television network has to convert that creation to a broadcast signal.
(3) A cable company has to convert the broadcast signal to a cable signal.
(4) The cable box has to convert the cable signal to a television signal.
(5) My television has to interpret and display the signal.

If any one of these 'stages' cannot handle HD, then I presume that a given
program would be disappointing when viewed on an HD television set.

If I were to purchase a high-definition television set, would it be a wasted
investment, or would I see everything in high-definition?

I suspect that the only thing that I would be able to enjoy in true 
high definition would be programming that is delivered by the cable company
on new cable channels that are specifically designed for high-definition.
Even then, I might be disappointed if the source (original) program
is not in high-definition. For example, "Gone With The Wind" was not
produced with high-definition technology, so watching it on an HD cable channel
would not be any better than watching it on my OLD television set.

Am I correct?  If a cable company hypes its brand new HD cable channels,
will ALL the programming on those new channels necessarily have true
HD resolution?

It is true that older programming, such as "Gone with the Wind,"
wasn't shot with HD in mind, but it will look much better in an HD
broadcast. 35mm films are higher-resolution than your old television
set is capable of displaying.

We received a 16x9 HDTV rear-projection unit for free when a warranty
repair to our old CRT set wasn't possible. The high-def programming
that we get from our cable company is terrific. I do wish more stuff
was available in high-def, but I'm very impressed with what is
available right now.

You will see better quality with a HDTV set, as long as you have a
source for the programming.  And currently there are several methods
of receiving that programming.

First off, if you get an HDTV set and a progressive scan DVD player,
you will see a higher picture resolution.  This is the because it will
put out the signal in 480p (progressive), versus 480i (interlaced). 
You can research the internet for the definitions of these
resolutions, but the bottom line is that you will have a clearer and
smoother picture.  Additionally, DVD's look great on widescreen TV's
as most DVD's are anamorphic, meaning that they are designed to fill
up the whole widescreen presentation.

For true HDTV, there are several sources available, but many of them
depend on where you live.  First off, you can receive HDTV programming
from the broadcast networks using an off the air receiver.  This
receiver may be built into the TV, but if not, you can use a seperate
decoder.  These signals look great, and are of perfect quality as long
as you have sufficient signal strength.  Best of all, once you have
the tuner, they're free.  However, the availability of these
broadcasts is largely dependent on your local broadcasters.  You
should check with them to see what they're offering.

Many, if not most cable companies in the US are offering HDTV
programming.  You will need a HDTV box from them, but it's just like
having a regular digital cable box.  In my local area, there are 9
channels, including HBO, Showtime, ESPN and ABC.  Additionally, many
are offering these with DVR's so that you can record the programming
and watch it later.

Finally, HDTV is available on Directv and Dish network.  Both of their
web sites list the channels available, but if I remember correctly,
there are about 10 channels per service, plus the networks. 
Additionally, Directv offers things like their NFL and MLB packages in
HDTV.  One word of caution on Directv...they are converting to a new
standard in a couple of years.  This new standard, MPEG-4 will greatly
increase their HDTV broadcast capability.  They will have network HDTV
signals for most markets and about 150 national channels by sometime
in 2006.  The bad part of this is that any decoder that you purchase
now will be obslete when they switch over to this technology.  I
believe Directv is planning to have an equipment trade in program.

Bottom line, if you buy an HDTV now, you should be able to enjoy it
long into the future.  You may need to purchase additional equipment
to support it, but you would probably have to do that anyway if you
waited.  They only question out there with new technologies like HD
DVD will be if they implement a copy protection scheme and your TV you
buy today doesn't have inputs for it.  I don't like that will be an
issue if you get one with inputs like HDMI.  Go ahead and get HDTV now
if you're interested.  You'll be hooked and never want to go back!

Hope that answers your question.  I'm not a certified expert, but I think I'm close.

Yes it is! At least that is the conclusion I recently came to.  Here
are my reasons:
1) In order to get digital/HDTV from my cable company would increase
my bill by around $40 a month.  I expect this cost will come down as
digital becomes the norm.
2) The cost of HDTVs are droppping rapidly. So if you wait you will
get more for your money.
3) Lastly, but I'm not sure of this, but if a program is not created
in HD it will look worse on your new expensive HDTV than it would on
your old analogue TV.