Hey everyone. I've got a kind of hard to phrase question here. The easiest way to explain it will be to just tell you what I'm trying to do...

I've used 3ds max to animate a falling spaceship that eventually "shatters" into a bunch of particles. Then, I'm overlaying this ship over a video clip so that it looks like the space ship lands on a building and explodes. What I've done in Max is have a simple box represent the building. When the ship "hits" the box, it explodes into particles. Particles that strike the box will go right into it and thus not be visable. This is what I need for overlaying the animatio over the video clip, because I don't want any particles do be in front of the building if the ship landed on top of it. So, now for my question:

I don't want that box to render out (because it would obviously obscure the building in the video clip). BUT, I do want the box to have the same effect on the particles (namely, make them invisible so that it looks like the building in the video clip is stoping the particles from going through it, or in front of it). How can I set Max render preferences or whatever so that I can hide the box, but still have it have the same masking effect on the particles?

I beilieve I once read somewhere that you can put geometry in a scene to create shadows and light effects and then not have them render out, but still have the shadows they cast show up. It would probably be a technique similar to that, right? Thanks for any help you can offer,