Last week, I wrote about the forthcoming service pack for Windows 7 and Windows Server 2008 R2. At the other end of its support lifecycle, is Windows 2000, which finally reaches end of life (i.e. the end of extended support) on 13 July 2010.
Windows XP remains on extended support for a while longer (until 8 April 2014) but service pack 2 (SP2) also goes out of support on 13 July 2010 and, from that date onwards, Microsoft will no longer support or provide free security updates for Windows XP systems running SP2 or earlier. Service pack 3 is available free of charge; however Windows XP users should really be planning on migration to a later version of Windows. For details of how to obtain the latest service pack for Windows XP, see Microsoft knowledge base article 322389.
Also, on 13 July, Windows Server 2003 moves out of mainstream support and into its extended support phase.  Service pack 1 for Windows Server 2003 was retired on 14 April 2009, so service pack 2 is required in order to remain supported. For details of how to obtain the latest service pack for Windows Server 2003 (and Windows Server 2003 R2), see Microsoft knowledge base article 889100. Windows Server 2003 and Windows Server 2003 R2 are subject to the same support lifecycle milestones as each other.
Windows Vista with no Service Packs installed will also lose support on 13 April 2010. Customers are advised to install service pack 2 for Windows Vista in order to remain secure and supported (although service pack 1 is still supported until 12 July 2011). For details of how to obtain the latest service pack for Windows Vista, see Microsoft knowledge base article 935791.
Customers running Windows Server 2008 have plenty of time left in their operating system investment, although Windows Server 2008 service pack 1 will be retired on 12 July 2011. For details of how to obtain the latest service pack for Windows Server 2008, see Microsoft knowledge base article 968849. The same service pack is applicable to both Windows Vista and Windows Server 2008.
It strikes me that all of this is very hard to keep track of, particularly for owners of small / medium businesses who often lack in-house knowhow.
This demographic, however, can often be slow to install updates and service packs, and some rarely do so at all.
Thanks for laying out the facts in a neat and concise way!