Eu tinha testado ele no max 9 e funcionava legal, depois do max 2008 em diante ele tem uma certa tendencia a travar o max quando estiver editando o material no material editor... a unica solução é trocar o render do material editor pro scanline, assim ele não gera um preview que é o que faz travar o max.
Segue umas informações que tinham postado na época no cgtalk, basicamente vc coloca o mapa no field opaque:
surface
This determines the material on the surfaces on the 'inside' of the volume, I used a material to shader and then put in whatever material I wanted.
clipped_surface
Same as above except it applies to the 'outside' of the volume.
step_distance
I think this determines the resolution of the volume, but it doesn't seem to have any visible effect although it seems to slow the render down at lower values.
threshold_opaque and threshold_transparent
Luminosity value at which the material becomes opaque/transparent
Fade_Depth
This is determines how much of the outside is faded, basically higher values make it look as though your volume isn't bounded by smoothing out all the clipped surfaces.
field_opaque
This is the map for determining whather a part of your object is opaque or transparent.
Edge_Fade
This turns on edge fading, controlled by the Fade_Depth value.
normal_type
This should be set to zero otherwise it gets all weird, I don't really know what it does.