According to: http://support.microsoft.com/gp/lifeselectindex [4], official mainstream support will end April 14th 2009 for Windows XP and Office 2003.
Extended support is available until 2014 and 2012 respectively for paying customers.
More info: http://blogs.zdnet.com/microsoft/?p=2365&tag=nl.e539 [6]
Links:
[1] http://pulse.veltsos.com/category/it/software/software/os/microsoft
[2] http://pulse.veltsos.com/category/it/software
[3] http://pulse.veltsos.com/category/it/support
[4] http://support.microsoft.com/gp/lifeselectindex
[5] http://linux.philosweb.com/drupal5/files/gp_lifecycle_bottom_2.gif
[6] http://blogs.zdnet.com/microsoft/?p=2365&tag=nl.e539