Well once in Activity Monitor use that to Quit the process.
Then use Spotlight to search for ANY Norton files. If you can find the installer .pkg run that and use the uninstaller within that package.... It should have a uninstaller ....
If not download
AppTrapp and run that. Once it is installed it will sit in the System Preferences and is un obtrusive.
Using spotlight again find the main Norton File/Folder and then drag it to the trash. Now this is where AppTrap comes into its own.
When you drag anything to the trash Apptrap chimes in and asks if you want to trash all associated files/folders to the particular
thing you trashed ....
If all fails you will need to install the Norton Software angain then go though the uninstall process using its uninstaller
Hope it helps some, if not post back and see what else pops up
Cheers
EDIT : And try what McYukon suggested 1st