I meant to post a note to this effect when I first heard the news, so, sorry for my tardiness. Anyway, if you're still running Windows XP SP2 for some reason, you won't be getting any more security updates from Microsoft, effective last week. This includes not only patches to the operating system itself, but patches to other Microsoft software, like Internet Explorer, as well.
If you have Automatic Updates turned on and you're a typical home user, odds are very good you're already running SP3. If you're unsure, you can check your version by right-clicking My Computer and choosing Properties from the pop-up context menu. Or, do Start → Run, type winver and click OK.
If you're bound and determined to stick with SP2 for the time being, Gregg Keizer has some tips for you. I can't stress enough, though, that it's very unlikely that your reason for sticking with SP2 is compelling, unless, say, you're on an office computer and your company's IT department makes the call on things like this. In other words, don't let inertia, procrastination, or fear of "breaking something" keep you from upgrading to SP3 -- it's painless and it is your first line of defense in keeping your Windows machine free from infection.