Windows 2000 Professional support runs out July 2010.
XP Extended Support is ongoing until 2014, or for two years after the next Service Pack, if there is one for XP before then. Mainstream support expired April 2009 making Service Pack 4 pretty much not going to happen.
Note that these dates do not mean the operating system will stop working, it just means there will be no new security updates, fixes, enhancements, etc. Over time the operating systems would become incredibly susceptible to various security holes, vulnerabilities and what not, with no fixes available.
The issue with Win2000 is not the OS itself, more the fact the web has changed and more and more sites and technologies use what is only available as part of IE7 and IE8, and those are only available with XP or later.