Maybe I don't get it right, but you need a photoshop or something like that?
Photoshop has its tutorial in it, which helps you to learn easily to use it. You can change parts of the picture by selecting them with a magic tool, which selects the same colouredpart, so like red-eye-effect and so on.
Never really seen anything like that, Steve. However, you might try asking any contacts you may have in the lighting industry, like mfgrs and mfgrs reps, etc. Seems to me like the only one's with resources and motive to develope software like that would be the lighting manufacturers themselves, so give that a shot.
Good luck, Radar
There are 10 types of people. Those who know binary, and those who don't.
Its not a quick solution but AutoCAD 3D and other 3D software will allow you to add lighting schemes to your drawings. This requires you to draw in 3D though. I doubt you can just scan a picture and get a 3D effect.
Programs such as Paint Shop Pro and Adobe Photo Shop allow you to create overlays which you could use to overlay a light fixture.
Perhaps if you used a image of a light fixture against a solid background you would be able to cut out the light pattern and overlay it transparently over another image. This would atleast give you an idea of what it would look like.