Alan, I got rid of my CS4 after updating to CS5. I still haven't figured how to install my Noise Ninja, however. I'll probably have to email the Noise Ninja people for instructions. I really haven't been able to test some of the new features to see if the improvements are worthwhile. I only upgraded because CS4 refused to recognise my new printer! (A problem which Adobe acknowledged!)
Just go to NN website and download the latest version you need. I upgraded to win 7-64 and got that version and installed. Just need your code and your good to go.