Mr Milk said..
Shouldn't the protection fees that I've been paying to Norton keep me safe?
No, not always. The Norton subscription tries to keep away the Malware and viruses that are trying to attack your machine, but there may be vulnerabilities in the actual code of XP that become known and are used by attackers to try and get access to your machine. As Windows is a huge bunch of code, there will be vulnerabilities that pop up every now and then and people rapidly learn how to use them.
I think in practical terms, if you only use it for browsing well-known sites, you should be pretty safe, but if there is a major vulnerability, you won't be protected. As everyone should, keep external backups of any data that you think is worth keeping, even if you have the latest version of Windows. You never know when your machine might break down.