Two Nikon SB-24s and one SB-800 placed behind the subject and bounced from the white back wall to achieve a long shadow and totally burn the white background. Strobes full power. Shot with Nikon D200 @ Nikkor 50mm. Strobes fired with radiotriggers.
Some photoshopping involved: Removal of the strobestands, minor darkening on the shadow and burning the backlight from the places it wasn't already burned...