The last official updates for Windows 2000 were released last year, 3 years after EOL, and were distributed inside the monthly security ISO update packages. Apart from that, a few more non-public official updates were leaked.
In case of Windows XP I'd expect at least regular official updates until July 2015 (when Windows 2003 is becoming EOL). After April you should definitely check the monthly ISOs available under this link:
Security updates are available on ISO-9660 DVD5 image files from the Microsoft Download Center
Just keep in mind that Microsoft will not mention the existence of those updates in their official news channels. As in case of Windows 2000, the updates can be found inside those ISO packages even though Windows 2000's name itself isn't listed there at all.
More than that, due to the fact that Windows XP is much more popular than Windows 2000, I'm 99% sure that a lot of non-public updates will be leaked as well.
I've downloaded 6 different months from the archive discussed above (starting with August 2010 and into 2011) and there are no Windows 2000 updates to be found at all. Each archive contains levels of folders with updates sorted by OS and language. There are folders for all the post W2K OS updates ( Vista, Win 7, 8, Server 2003 and 2008) but not a single folder in any archive for 2K updates, Not a single individual 2K update I can find anywhere in the August 2010 and year 2011 archives I have extracted.
Tomasz86, you said that MS produced W2K updates for 3 years after EOL for 2K (which was July 2010. Then there should have been MS privately issued updates for 2K until June 2013-I realize not every individual month will have updates.). I cannot find any of them in the half dozen archives I have checked.
(I can clearly remember, there were no updates issued in July 2010 for 2K but quite a few were issued in August 2010 for XP. I would think at least some of those would have applied to 2K but only available privately to those corporations who paid for the continuing post-EOL support.)