I'm a geek and have actually seen this movie (I rented it, tho). The movie itself isn't that great...but I was so happy to see the story made into a movie b/c it made much better sense then. (Keep this in mind when you read what I've written below...you'll understand why I was happy that it was made into a movie)
See, it's about this necklace that caused a scandal in the French court, esp. with Marie Antoinette, at a time when she could little afford a scandal. This jeweler made a necklace out of a zillion $$ worth of diamonds (It actually looked like the one in the picture above). He made it thinking that someone at court would want it--Marie or even the king for his mistress. Well, King Louis didn't want it...and Marie didn't want it b/c it was "seconds" if her husband was initially supposed to buy it for his mistress. The jeweler was out a LOT of money and was desperate...so he got caught up in this scandal involving a member of the church and this woman. Crap--I can't remember this very clearly--it's really confusing!
Anyhoo, the woman (Jeanne...de la Someone) ends up stealing the necklace by tricking the Cardinal Someone into thinking that Marie Antoinette loves him so he buys the necklace for her. MA in fact hates this cardinal and knows nothing about the necklace. But "the affair of the necklace" becomes so scandalous when it goes public that Antoinette takes the brunt for it (the people of France can't believe that she would NOT want the most expensive piece of jewelry ever made...so they believe that she had a hand in making it, buying it, and raping the French people over the coals to pay for it).
So...I'm sure that completely confuses everyone. Oh, and Chris Walken plays this Russian (or Prussian? or German?) conman who knows about the necklace and what Jeanne does to get it.
OK, note to self: remember plots of movies better so as not to embarass myself again!