Registry hackers discovered it may be possible to receive free updates for Windows XP until 2019 by changing a few registry entries in the operating system to make the operating system identify itself as Windows Embedded POSReady 2009 to the Windows Update service.
Windows Embedded POSReady 2009 is based on the Windows XP kernel but it's unknown if these updates are 100% compatible with Windows XP so use this at your own risk or upgrade to a more modern operating system. Chances are high that Microsoft will eliminate this loophole pretty quick though. You can find the full details of the registry edits over here.
The trick works on 32bit and 64bit. POSReady 2009 is based on the Windows XP kernel and is officially slated to receive updates until 2019. Microsoft, on the other hand, has not offered a comment on this workaround. Word on the street is that this workaround will be impossible fairly soon so you would have to be quick.