Interesting reading the Old Mister Crow approach and then Lanhua's approach. For cataloging my orchids I use a ring flash on a Canon 40D. That way the color is the same on all images and there is no shadow. Great for detail close up, and I set the shutter to 1/250 so no backgroundlight comes in.
I was talking to my cousin about getting a high power studio monolight set up and he reminded me that with a digital camera you can use Compact Florescent daylight bulbs and set the temperature to match in the camera. That way you can do the set up on the cheap. Use one lamp for the photo with a reflector on the opposite side to compensate for a light shadow and then another light to light up the background to remove any shadow if you aren't using a black backdrop. Simple and cheap. Use black velvet for the cloth and most of the shadow disappears. Works for lighter colored orchids.
Always think about the light not the camera and you'll be better off..imho