I need to create a scene with a film projector, projecting film footage against a screen - Can anyone tell me or point me towards a tutorial how this is achieved? I can already project an image from a spotlight but I can't seem to create volumetric light rays.

You can find this example in help:

http://www.sidefx.com/docs/houdini11.0/examples/nodes/shop/atmosphere/AtmosphereShader [sidefx.com]

And this post:

http://www.sidefx.com/index.php?option=com_forum&Itemid=172&page=viewtopic&t=21190&start=0 [sidefx.com]

And this post too:

http://www.sidefx.com/index.php?option=com_forum&Itemid=172&page=viewtopic&t=17462 [sidefx.com]