Chris:
Have you tried using a 32-bit targa (TGA) file? I
was working with alpha channels back and forth between
PovRay and PhotoShop and found that PNGs didn't work but
32-bit TGAs did.
To make and save a TGA with an alpha channel in
PhotoShop is a PITA but it *is* possible and povray reads
the resulting file correctly.
Pete
