Taken from http://en.wikipedia.org/wiki/Windows_2000
Windows 2000 has now been superseded by newer Microsoft operating systems: Windows 2000 Server products by Windows Server 2003, and Windows 2000 Professional by Windows XP Professional.
The Windows 2000 family of operating systems moved from mainstream support to the extended support phase on 30 June 2005. Microsoft says that this marks the progression of Windows 2000 through the Windows lifecycle policy. Under mainstream support, Microsoft freely provides design changes if any, service packs and non-security related updates in addition to security updates, whereas in extended support, service packs are not provided and non-security updates require contacting the support personnel by e-mail or phone. Under the extended support phase, Microsoft continues to provide critical security updates every month for all components of Windows 2000 (including Internet Explorer 5.01 SP4) and paid per-incident support for technical issues. Because of Windows 2000's age, Microsoft is not offering current components such as Internet Explorer 7 for it. They claim that IE 7 relies on security features designed only for Windows XP Service Pack 2 and Windows Vista, and thus porting to the Windows 2000 platform would be non-trivial. Microsoft is strongly advising all users still running Windows 2000 Professional and Server to consider upgrading their operating systems to current operating systems for increased security. While users of Windows 2000 are eligible to receive the upgrade license for Windows Vista or Windows Server 2008, neither of these operating systems can directly perform an upgrade installation from Windows 2000; a clean installation must be performed on computers running Windows 2000.
All Windows 2000 support including security updates and security-related hotfixes will be terminated on 13 July 2010.
Windows 2000 has received four full service packs and one rollup update package following SP4, which is the last service pack. These were: SP1 on 15 August 2000, SP2 on 16 May 2001, SP3 on 29 August 2002 and SP4 on 26 June 2003. Microsoft phased out all development of its Java Virtual Machine (JVM) from Windows 2000 in SP3. Internet Explorer 5.01 has also been upgraded to the corresponding service pack level.
Many Windows 2000 users were hoping for a fifth service pack, but Microsoft cancelled this project early in its development, and instead released Update Rollup 1 for SP4, a collection of all the security-related hotfixes and some other significant issues. The Update Rollup, however, does not include all non-security related hotfixes and is not subjected to the same extensive regression testing as a full service pack. Microsoft states that this update will meet customers' needs better than a whole new service pack, and will still help Windows 2000 customers secure their PCs, reduce support costs, and support existing computer hardware.
Although Windows 2000 is the last NT-based version of Microsoft Windows which does not include Windows Product Activation, Microsoft has introduced Windows Genuine Advantage for certain downloads and non-critical updates from the Download Center for Windows 2000."