Samantha, first of all if you use flash you don't actually have to shoot in the dark. Nobody likes fiddling in the dark with expensive equipment..
Just use a smaller aperture and low ISO to get rid of the ambient light, then pump out a spotlight with the flash.
Bad example I found from my shots:
This is Canon 7D with ISO 100, f/14, 1/320s and shot in the middle of the day, indoors. The room was not dark at all, window shades open etc.
The light source is a (relatively) cheap Elinchrom D-Lite2 studio flash with a grid to focus the light. It's quite close to the "model" and at low power which also helps to reduce the amount of light reaching the floor and wall behind him. There's no post processing in the shot to remove them.
You could do it with a smaller flash and a snoot+grid for example when indoors. These are available on ebay for pretty cheap. Outside with the sun shining you would need loads of power for the flash and ND filters to reduce the amount of light coming in through your lens.
I would not try this with continuous (non-flash) lighting, you need a LOT of watts and will create a LOT of heat.
---8<---- Don't worrry if you don't understand what's below ---8<----
I know I shouldn't use 1/320s with the 7D and studio flash.. but I didn't think the shutter shading the bottom of the pic would hurt at all here (cropped from a landscape pic).