Uncovered Windows XP Registry Hack Allows Continued Free Security Updates From Microsoft
“The workaround makes use of updates for Windows Embedded Industry (formerly known as Windows Embedded POSReady),” wrote Wayne Williams of Betanews. “This is based on Windows XP Service Pack 3, and the security updates which are being released for it are essentially the same ones Microsoft would have pushed out for XP, if it was still doing so.”

(Credit: Betanews)
Next, you have to create a text document in the registry and paste in the following text:
Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SYSTEM\WPA\PosReady]
"Installed"=dword:00000001
“That’s all you need to do,” added Williams. “Windows will now automatically fetch updates designed for POSReady 2009, ensuring XP remains protected for the foreseeable future.”
And so the legend of Windows XP continues.