There is plenty of free security software on the net, most of it just as good (sometimes better) than Norton.
I run all the following:
AVG Anti Virus. They do sell a version, but there is a free version for home use.
Zone Alarm Firewall. Again, they do sell a version, but there is a free version.
Adaware - Checks for spyware. Free
WinPatrol - monitors your PC to make sure nobody is trying to install a program or change your internet settings without you knowing. Free
I use all the above, by there are other programs lke Spybot Search and Destroy which looks for spyware.
Dont let PC World convince you that Norton is better than these free products. These products win many head-to-head tests in PC magazines.