to produce a software with high quality consistently is 
more desire than a need. thats when qa comes into picture, 
QA invovles in the entire software development process- 
monitoring and improving any agreed up on standards and 
procedures and ensuring they were dealt with 
  QA is more abut "prevention"
eg: In preventive approach QA"tests" the requirements 
specifications before developers start design and coding. 
It removes any obvious ambiguities and omissions in 
requirements in the very early  in the life cycle saving 
time and money for hte company.

Quality Assurance as the name suggests is to follow the 
steps and the methodology that will ensure that the end 
product that is delivered is of high quality.

QA consists of process, setting methodologies, inspections, 
walk throughs, surveys and meetings. Internal Audit is not 
a part of QA and should not be mixed either. But similar to 
it processes are laid down to ensure that the approach and 
the tools and the manpower that is employed and set for 
validation will result in high quality product. Training 
for every tester to make that more sound is a part of QA.

Hope that helps !