free avg anti virus is FREE and better than most you pay for, depending on your equipment, you will not need a software fireweall such as the one built into Nortons.
If you have a wireless/wired router, such as a belkin, netgear, linksys, etec etc it will have a firewall built in, make sure this is turned on and, it should be by default but check, if you do forget another firewall cos it will slow your internet down using two.
You do require a firewall on your computer, the one in your router is a inbound firewall only (as standard) a decent software firewall on your computer will stop nasty programs making outbound connections.
this has been answered about once a week on here forever, do a search on free anti virus in the search up there ^ (select site)