Photoshop 6 can't read Camera Raw files. The RAW in PS
is a different file format. Photoshop 7 needs the Adobe
Camera Raw extension. Photoshop 8 has it built in.
To work with Photoshop 6, simply use the Canon conversion
tool that came with your camera. Export the converted file
as a .tif and open it in Photoshop. The Canon converter is
a bit slow, but it does a very good job.