See 4.11.1 first paragraph.
"The supplier shall ... control, calibrate, and maintain inspection, measuring and test equipment (including test software)..."
I had to address this for my Coordinate Measuring Machine to prove that the mathematical algorithms were correct. I just called the manufacturer and this is apparently standard practice.
I also noticed the the QS9000 PDF files available on
http://Elsmar.com/pdf_files/ had a good section on Design (EOP-04-01, Sec 4 "Design Aids and Methods" which says:
"Computer software used for carrying out calculations and other design activities is qualified and approved". It goes on to say the various funky ways of qualifying and approving -- including getting a certificate from the s/w manufacturer.
Doug