In December 2004, Microsoft announced that in 2005, Microsoft will discontinue the free support for Windows NT. I think that Windows Serviceability Team works on these support issues. For a complete news see http://www.techbuilder.org/news/59200477 or use google :).
I have read this news before and was confused that when should a developer or a development company should stop wasting useful resources on older operating systems and tools. While browsing through the MSDN, I found a link that expalins the Microsoft's Policy. By reading this FAQ, you can safely analyze that when a product is 10 years old, then its almost the time to say bye bye. See the FAQ at http://support.microsoft.com/gp/lifepolicy for a complete overview.
Also have a look at http://support.microsoft.com/gp/complifeport to see the exact dates after which the support will be available for a price to big clients.