Quote - > *Quote - Tom, You can create an infinite plane, or an infinite slab. For the volumetrics, you need slabs. To create a slab, simply hold the mouse button for a second over the water or ground or cloud primitive on the create shelf. you will see options for surface or volume. Hope this helps.

Thank you...  I did try that but the slab was not behaving like in the tutorial..  Also he must have been working with some volumetric cloud file...  I can not find such a cloud in the contents...

Try looking in the Pro Materials..(provided  from David Brinnen).There are some volumetrics there.

In fact the whole of the material provided right there in that section are terrific..