i think you should definitely uninstall old norton antivirus but it could be a litle bit tricky. you can find a lot of artickles about how to get rid of norton antivirus. its actualy an their website.
dont know about ghost but i think you will have to uninstall it separately. just use control panel/add and remove prog. than you can try to load new program hope u have good comp othervise your comp will be slowed down by norton. i dont say its not good program i have used it before but wouldnt use it again.
good luck and if any probs just post back