IMHO, anything lol.
If it's Norton Internet Security, it also includes a firewall.
I assume this means you already have Norton installed?
If I were you I'd use it till my license ran out and uninstall it using patio's "public service announcement" guide y see), then install AVG anti-virus, a selection of anti-spyware programs like the ones mentioned above, and Sygate Personal Firewall.
All free, and will keep your system very secure.