One of the worst things that could happen to your XP installation over the next couple of years would be a virus or spyware infestation. In the most serious cases, the only way to disinfect your PC is to perform a total operating system re-install, which is not an enjoyable experience. To avoid this scenario, you should arm yourself with a few protective utilities.
One popular and free choice that's easy on system resources is AVG Antivirus Free Edition Once downloaded and installed, AVG will sit in the background monitoring your PC for dangers, including viruses, spyware, phishing websites and emails containing suspicious attachments.
If you already have adequate virus protection, it's still worth bolstering your defences by installing some spyware protection. Spybot Search and Destroy is another free tool that, thanks to regular updates, will keep your PC safe. Alternatively, you can purchase one of the many commercial internet security suites available, which provide anti-virus, anti-spyware, firewall protection and more, all in a single package.