I don't know if I should mention this here, but I had a laptop running XP lying around as a spare system. I installed OpenSuSe after XP death day in April but various members of my household felt scared by Linux so I made it dual boot OpenSuse/XP SP3 and just out of curiosity I tried the widely known Point Of Sale registry trick. You can fool Windows XP into thinking it's the Embedded Industry version, which is designed for point-of-sale (POS) systems and will (apparently) continue to receive support until April 2019. This is what I did:
1. Open a blank text file in a text editor e.g. Notepad
2. Paste in the text below
Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SYSTEM\WPA\PosReady]
"Installed"=dword:000000013. Save the file somewhere with a .reg extension - for example xp.reg
4. Find the file in Windows Explorer
5. Double click it.
6. Answer Yes to the prompt.
I restarted the machine and saw that the Windows Update notification was showing 74 updates available (this was Aug 15 2014 approx; not updated since XP end of life date). The only ones that failed were definitions for Microsoft Security Essentials so I installed Avira Free. I have been notified of more updates since.
Disclaimers:
a. Modify the registry at your own risk.
b. Nobody knows if Microsoft will disable this loophole, although doing so would probably disable the many point of sale systems using XP It seems to me if you are going to make XP stagger along a bit longer you may as well get whatever updates are going.
c. Maybe some POS updates would interfere with a regular XP PC although mine seems fine so far.
d. Microsoft are aware of the trick, and say that security patches obtained by this method may not have been tested against regular PC style XP, and that users should really update to a supported OS.
e. Only suitable for 32 bit systems, although apparently there is a workaround for 64 bit systems here (I have not tried this)
http://www.sebijk.com/community/board9-community/board5-pc/2985-getting-xp-updates/?s=50e2f202ba293eb33974b075c6ce5b4b21ee1963f. If someone was thinking of doing this they should probably do some Googling and evaluate this option for themselves.