Then after using the removal tool look through the entire c: drive for files and folders left behind by the "removal" tool and then trawl through the registry for every single reference to "Norton", "NAV", "Symantec" and "NIS" (if it's Norton Internet Security).
Unless things have changed since I last had to rip out a Norton Internet Security installation a couple of years ago, you will find the "removal" tool does NOT dio what it says on the tin.