I thought I'd briefly show the set up that I used for the Splashing Pepper photograph.
I used a sheet of A4 paper as a makeshift Snoot for my SB600 flash. The snoot helps to direct the light onto a smaller area so that the falling object can be isolated. I used one of the excellent 'gorilla pod' tripods to attach the flash to my kitchen tap... handily located to support the flash at about the right height.
It's not very dark in the kitchen where I set up but it doesn't need to be as long as the camera is set so that the exposure (without flash) does not expose any of the ambient light. In the case of this shot the aperture was set to f16 and the shutter to 1/1000 of a second which will expose the scene as pretty much black.
You can see the position of the SB900 pointed at an angled white board. The SB900 was set to 'master' and the SB600 as slave so that it was fired. I used a sync cord to connect the SB900 rather than my cactus triggers as I needed the 'high speed sync' capability to expose correctly with a shutter speed of 1/1000 of a second.
Here is one of the shots from this shoot