You might want to ask this on rec.photo.digital, which is a much more active
group, but be prepared for some "religious" discussion concerning the
"meaning" of the word macro.

In a pedantic and technical sense "macro" means that the image on the sensor
or film is the same size as or larger than the actual subject.

In a practical sense, what a macro lens will do that a telephoto won't is
let you get relatively close to the subject and thus fill the frame with a
smaller portion of it.  Macro lenses also as a rule have relatively low
distortion.

You can use extension tubes or a bellows or a "close-up" diopter to get
similar degrees of magnification and can correct reasonable amounts of
distortion using Photoshop or other image editing programs, at the cost of
some degree of sharpness.

As to subjects, flowers, insects, seashells, pebbles, anything small that
will let you get close.

The big difference between a telephoto lens that's not macro and a macro
lens is that the macro lens allows you to focus much more closely to the
lens than a conventional tele.  Being able to focus on an object close
to the objective lens makes it possible to have an image on the film, or
sensor, which is life size, or larger.  That's a macro image.  Whether
what you create with it represents nature, or not, is a different question.

    -Raf

Classically, Macro Photography was a photograph of an object taken at
1:1 magnifaction or greater (that is life size).   Dispense with that
notion.  It commonly is used to refer to close up photography.    Back
in ancient history (the 60's and 70's) a Macro 35mm lens was generally
used to refer to a lens which had between a 1:1 and a 1:2  reporduction
ratio at its closest focus.   At 1:1 a bee photographed on a flower,
would be the actual size on the negative or slide that it was in real
life. at 1:2, the bee would be half its real life size.  Macro lenses
were also gernerally corrected for flatness of field.  ALL normal lens
have a curved field.  That is the, the focus plane is not the same
across the entire width of the lens.  On really good lenses, this
curvature of field is minor and we consider the lens to have excellent
edge to edge sharpness.  When photographing 3-dimensional objects more
than a couple of feet from the camera, these issues are not visible.  
However, when taking a close up  of a coin, at 1:1, this curvature of
field is an issue.  So, true macro lenses contained elements to correct
this.  This holds true for fixed length macro lenses for SLRS'' (i.e.
Nikon, Canon, Minolta, Pentax etc.)

Then life got muddied.   The marketers got in the way of engineering.
Some bright bulb discovered he/she could add 50 bucks or more on the
the price of a zoom lens by adding a "macro" setting.  At best, that
really was a closer focus lenses than the equivalent non-macro version,
at worst is was printing on the box, and extra engraving on the lens
barrel, but no real "macro" added.   Again things progress.   The
computer engineering that was not available to the lens designers of
y'or, allow todays engineers  to produce zoom lenses which have
credible close focusing capability. Notice, I did not say macro.  
Compensating for curvature of field is , I don't believe, yet possible
in a complex zoom lens.

I own two macro lenses.  On is the Nikkor 55mm macro (which Nikon
confusingly calls micro) and the Nikon 105mm F4 macro (also confusingly
called micro).   The flatness of field in the 55mm is extraordinary.  
However, at 1:2 with the lens,  the front of the lens is about 2 inches
from the subject.  Makes photographing bugs nearly impossible.  I don't
know of any "cooperative" bugs or bugs holding out on a modeling
contract (and hense cooperative subjects  <g> )  The distance doubles
with 105.  It is much more convenient for wildlife photography. Better
yet would be the 200 Micro.

The other issue is lens speed.  At macro range, or even close focus,
the depth of field is very shallow, measured in fractions of an inch.  
You need a small aperature to compensate.  Even then, its still
fractions of an inch.   Also, focusing at close distances is tough,
even for AF systems.   Most zooms do their "macro" at the full zoom
extension.  If your zoom is a variable aperature, this means the thing
may at F4.5 or 5.6 (or worse).  F4.5 is marginal for focusing
accurately at close focus, and for my eyes F 5.6 is impossible.

What do you need?   Certainly you can take lots of great flower shots
with a decent close focusing telephoto or zoom lens.  With some work
and careful selection of subject you can take some amazing ones.  Bugs?
or other small objects, I would opt for a 100mm or better true macro
lens.  The choices will depend on your camera brand.   Taking really
good macro shots requires time and patience and every issue that
effects every photograph is magnified greatly.  You might as well
remove one thing form the equation and get a decent macro lens.   BTW
there is an added benefits. Most 100-110mm macros are F2.8 or there
abouts.  The 100mm focal length makes a great portrait lens on 35mm and
an OK one on 1.6x digitals. The faster speed makes for some better low
light portraits and because of wide aperature, it is easier to throw
the backgorund out of focus.... dual purpsoe lens.

Sorry for the long essay.. I hope it was of some help.