Peter Lyons , Jan 18, 2007; 09:18 a.m.
One way I've heard of doing it is to make yourself a "light tent" over the jewelry, with a single opening for the camera lens. Use a translucent white material and light it from the outside-- just place your own studio lights around the tent to give the most even coverage possible over the whole tent. This way the jewelry will have lots of shine and no dark spots.
have fun! Peter