Kirk,
Thanks for the reply.
Apparently CS3 uses Planar by default, rather than interleaved. (I am not using any compression, though) You learn something new everyday.
From the help PS files..
"Pixel Order
Writes the TIFF file with the channels data interleaved or organized by plane. Previously, Photoshop always wrote TIFF files with the channel order interleaved. Theoretically, the Planar order file can be read and written faster, and offers a little better compression. Both channel orders are backward compatible with earlier versions of Photoshop."
Peter