Hi,
Good job in moving away from Norton - in my view it's a pretty bloated piece of software that you can do without.
As for free alternatives, there are a few options available to you. I always used AVG Anti Virus Free Edition - both for myself and for the students that I teach. However, after reading this article -
PC Pro: Product Reviews: Labs: Antivirus software - I switch to Avira Antivir.
I'm sure other members of the forum will have other ideas, but that is my two cents...