STL Import and Rendering

[b4a5r0t]

I'm working on a project that needs very photo-realistic renders of the compleated assembly including the product that will be in it. I've been using Inventor for modeling and Showcase for rendering but here is what the problem is. The product that is to be placed in the assembly is a head of lettuce. I have it as an stl file since thats the only format I could find it in and looks quite good. I can open it in Inventor as well as Showcase without problems but once I try to do anything with it thats when the problems start. In Inventor I cant apply any constraints or materials but when I place it in to the assembly and just kind of put it where its suppose to be for rendering there is no way to apply material apperance settings. I can do it in showcase when i open the stl by itself but if i open the assembly that has the stl in it the stl just dissapears. I tried importing it into inventor using the stl import add-in but due to a ridicously high polygon count every computer i tried to do it on crashes. Also found a way to conver stl into sat file using 3dsMax that works with lighter stl but this one crashes it as well. Like i said i only need it as a representation of a product so its the rendering abilities that count. Does anyone know of any other way to do this?  Also if you have a model of a lettuce (doesnt need to be any specific kind, actually any leafy greens will do) that can be used in the way that i need i would really appriciate you shearing it. I will post updates as i figure more of this out but as of now i have no solutions and need to get the project done. thanks in advance! 

ps

i tried attaching the stl but cant since its an stl, if anyone is interested in it i can email it no problem, i found this file on the 123d liblary