Since you already have NAV 2006, stick with it to see how it does. I'm sure it will do a great job protecting your PC. Otherwise, why would Norton release a new AV already? Unless they're becoming like Microsoft, haha, yes I made a funny.
As far as NAV 2005, I'm using it too and it's been as great as Christmas. Works wonders. I get my automatic updates, no freeze ups, no conflicts with any other programs, it's just peachy.