The Six Sigma methodology DMAIC (Define, Measure, Analyze, Improve and Control) is used to improve an existing process.
Design for Six Sigma is used to design a new product or service.
The methodology used is DMADV (Define, Measure, Analyze, Design and Verify).
Define the goals and customer (internal & external) requirements. What is Critical to Quality.
Measure customer needs and specifications this should include benchmarking competitors.
Analyze the options.
Design the process.
Verify the design performance and ability to meet the customer requirements.
DMAIC was discussed in earlier blogs:
http://www.housingzone.com/blog/part-1-basics-process-improvement