I PM'd a guy on a photography board who's company photographs jewelry for a living. His reply:
"Greetings,
Fortunately I don't photograph jewelry for a living but my company does.
When you mentioned a light box are you referring to a traditional light box for viewing slides or a light diffuser solution such as a Red Wing or Lastolite with a lighting source? Three lights provide the best effect with two at the sides and one from above and slightly behind to get good highlights. This is probably the most difficult to master.
Costume jewelry is much more difficult to photograph than real gem stones due to light diffraction and impurities so diffused lighting is paramount. Using a camera with a good sensor makes a big difference we used to use three shot Leaf cameras to do this but those are long gone and currently do this with PhaseOne P20's on Mamiya 645 bodies. I would probably look at a D50 over the D40 and get the DK-21M or DR-6 eyepiece to save her eyes and back. For a lens the Tamron 90 or Nikon 105 (non VR) would be a good choice since the 85PC is well out of the price range. The P&S route has some good and bad points which include; greater depth of field due to the focal length, aperture tops out at around f8. noisy sensors above 5 MP. So the key for this is finding a P&S that is around 4 or 5 MP with a large sensor. Going through DP Review could probably help in narrowing a search for this and then looking at the image samples.
With all that said the next factor is post processing and this varies depending on web or print needs so the images don't look flat. If shooting gold then adding some black to that will help the definition. Depending on your costume jewelry you might be dealing with multicolored specular highlights that will require some masks to be cut, this is the most frustrating aspect of shooting costume jewelry.
For used equipment, B&H, Adorama and KEH are all good options.
Good luck and let me know how it goes,
marc"
Also- note the well thought of links at the upper left corner of the Macro World forum under "Macro World Resource." And came across this:
http://www.tabletopstudio.com/documents/jewelry_photography.htm