Hi,
you can see the highlight warning while reviewing an image by pressing the "DISP" button, each time you press "DISP" the view on the preview screen will cycle through varying amounts of info shown(eg. Histograms, ISO, shutter speed, aperture...). Any highlight warning will show as a flashing area on the image.
I think you can get a preview of highlight warning if you are shooting in live view mode but this is only a guestimate.

      Histogram is graphical representation of the picture in terms of black(0) to white(255). The Left Wall (End) is Black  (0) and the Right Wall (End) is White (255).  If you see the white line (activity) towards your Left Wall (Black) more, then your picture is Under-Exposed. If you see the white line (activity) towards your Right Wall (White) more then your picture is Over-Exposed. A correct exposure is attained when the graph (white activity) is in the middle. Normally, many accept Under-Exposed pictures (Not the totally Under-Exposed ones) but not the Over-Exposed ones.
   
     When you Highlight the Histogram with you picture by the help of the display (DISP) button you can see the the Over-Exposed parts of the picture blinks. So to attain the 'correct exposure' obey to the green dot that you see in the optical viewfinder. When the green dot blinks, you can understand the it is not the correct exposure. The aperture/shutter speed display also blinks, telling you to correct it accordingly.
 
      Another histogram (RGB) that you see with the help of the display (DISP) button represents the amount of Red, Green and Blue, respectively, in your picture.

Hey Tartlaghan - here is a nice read if you want to really start to understand the histogram.

http://www.cambridgeincolour.com/tutorials/histograms1.htm

I do think it is worth it to really understand the histogram.

Actually,
To be exact; a histogram with most of the info towards the right isn't over exposed necessarily...it just means that the distribution of tones is more towards light than dark. (such as your car in a snow scene).

It really doesn't mean that it's over exposed or under exposed or that having a big lump right at the middle is good either.

Notice that in this picture the distribution of tones is highly favoring white, so the histo is right-skewed. Its' not over exposed at all. I metered it with a hand-held.

CTWO...

Nope...a histo ONLY shows "distribution of tones."

Take a pic of an 18% grey card...they'll be dead in the center if you properly expose and your camera meter is accurate.

See this link and check out the section called "high key and low key"

http://www.cambridgeincolour.com/tutorials/histograms1.htm


Check it out.

Same exposure; see the meter on the left in each pic....but notice the histogram skewing.

Thanks - I kind of get it!  Time will tell!!!!!

Good! That's great to hear.