Just a quick thought, I maybe worth while to run the Norton Removal Tool. Link Download Norton Removal Tool 2010.0.0.98 - A program that can remove some Norton software from your computer - Softpedia
This removes the "bits and pieces" that the bundled Uninstall in Norton forgets
I would suspect that the Vista version may work. Norton has a habit of leaving "bits" in the MBR. Would have to be the worst security suite I have ever played with. Having said that, I am sure I will ruffle some feathers.
When Peter Norton first wrote the programme it worked fine. But like most other Antivirus suites they put too much in. Very difficult to configure.
I run Avast and Comodo on seven computers with XP and Windows 7 with no problems (and they are free).