Microsoft will not provide security fixes for XP after April. That means that you will live in a Day Zero* world, forever. So what to do, assuming that you don't want to throw away your computer (which is still working)?
Here's a thought: upgrade to Linux:
I decided it was time for me to let go. I gave Ubuntu 12.04 a shot. My computer felt modern again… except for that damn Unity UI. Why do all my apps have to be full screen? My netbook is not a tablet. And that Ubuntu Software Center is quite large and annoying. I dove in to a pile of configuration files to fix these problems and decided I got tired of fooling around with it. I stuck it out for a few months before giving up and giving Linux Mint 14 with Cinnamin a go, and now I am very happy. The only thing I needed to do post-install is get Google back in to my Firefox. A 5 minute fix. Not bad.apt-get install is the shiznit. There are GUI based install managers that will search for and find apps and then install them. And you don't need antivirus.
My Linux Mint experience has moved closer to my more expensive Mac experience, except Text Edit has been replaced with gedit. I actually like gedit better. It doesn’t scream at me to go to iCloud to just fiddle with a file. Also, “apt-get install” is vastly superior to launching the Mac Store.
My mainframe here at Camp Borepatch is an old Compaq dual core/2 GB RAM beast. It's quite snappy on Linux, because it doesn't get cluttered up with defrag and indexer and all the other junk. Every now and then I might have to kill the plugin-container because Flash is an abomination before the Lord, but that solves it - with Windows I'd have to reboot to clean up the memory leakage. And dig this:
Back to comparing with XP, the only slight drawback I see is that Paint.NET works better than Pinta, but I am willing to make that trade. With XP gone, I get modern memory management and a modern file system. Thanks to ext4, I no longer have to worry about defrag. I am pleased to let go of my virus scanner too.
My little Atom-powered 1 GB RAM netbook feels much faster.
Ted@Borepatch:~$ uptimeTry that on Windows, suckas ...
up 75 days, 9 min, 1 user, load average: 0.95, 0.89, 0.89
Were I to install a new distro, I'd also go with Linux Mint (just back up your Windows data to USB before you upgrade). Or you can buy a new computer. Hey, it's your dough.
* A Day Zero security bug is a vulnerability that is discovered and announced (and typically exploited) before a fix is available. It's the worst sort of security problem, because there's no way to defend yourself even if you want to.
UPDATE 15 January 2014 20:50: R. K. Brumbelow points out in the comments that Microsoft announced late this afternoon that they would extend the XP support window to next year. You should still upgrade. It's very unlikely that they will extend it again. The issue isn't going away.
UPDATE 15 January 21:18: The extended support is only for the Microsoft antivirus/antimalware. The security patches stop in April 2014. So you will in fact be living in a Day Zero world, relying on Microsoft antivirus to make it all OK after the Bad Guys pwn you longtime. Start planning your move, whether it's free to Linux on your current hardware or to Windows 7/8 on new hardware. Or to a Mac, if you're rolling in dough.