There are two ways to do it. First shade your object so that color = 0, transparency = 100, and no light interactions when fully transparent is checked. Next you have two options with the lights, either turn off Lighting through transparency on the renderer or if you need that, soft shadows don't work with transparency so set your light to soft shadows instead of ray traced. Good Luck, Eric Winemiller Digital Carvers Guild Freeware and commercial 3D extensions http://digitalcarversguild.com

Eric Winemiller
Digital Carvers Guild
Carrara and LightWave plug-ins