So WindowsXP ended its mainstream support cycle around 2009. It's only been receiving security updated since that time and they're scheduled to shut down around April 8, 2014.
Moving off of WindowsXP in favor of a more modern operating system (Windows7, Windows8, Mac OSX, or Linux) would be greatly desirable. The longer time goes on beyond April, the more at-risk your machine becomes. XP is a vulnerable operating system.
But let's pretend for a minute that you wanted to keep XP for a while longer? What would happen? Will is just stop working?
No, actually. It will keep working as it had been. Here's some of the risks though:
1. Over time, your system will become increasingly more vulnerable to threats that emerge beyond April 2014.
2. New software won't be made for XP, so content from stores or delivered over the web will stop working for you over time.
3. New antivirus definitions won't be shipped to you and will also increase your vulnerability.
4. You will become a target. Virus writers know that humans don't like change and that you're hanging on to that old machine, and they'll write code to exploit the fact that you're still using it.
5. New hardware isn't going to work because OEM's won't be writing driver software for them on the XP platform.
Sure, it'll continue to work, but staying on XP won't be a great strategy for a business looking to meaningfully control their technology risk. Doing so will only exacerbate the risk. And if you're running any kind of point of sale (POS) software on this platform, you'll fall out of PCI compliance, further putting your firm at risk.
if you own a business, don't take chances. Replace the XP box at your earliest opportunity. Regrettably, there's no upgrade possible here ... The box pretty much needs to be replaced. Talk to you tech professional for getting this done before too much time goes on beyond April.