Microsoft will officially retire support for Office XP and Vista's first service pack according to published plans on July 12 2011. That's the last date you will be able to get security updates for these older products.
Microsoft supports business products for 10 year cycles, with the first five years in what they call 'mainstream support' and the second five years in 'extended support'. The difference is that in extended support non-security fixes are paid for.
If you use Vista you can continue to receive security updates by upgrading to Service Pack 2 (SP2) which was released in May 2009. If you are running Office 2003, Microsoft will continue providing extended support until April 2014.
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