We all knew this day was coming, mainstream support for Windows Vista will end on April 10 with Office 2007 receiving the same fate today. Windows XP and Office 2003 will enjoy another two years before being cut.
Microsoft divides its support lifecycle in two stages: "Mainstream" and "Extended". Within Mainstream, software receives the full range of free security updates, stability improvements, bug fixes, and occasional new features. Within the Extended phase, only security updates are made available, though companies with paid support contracts can receive other fixes.
Currently, Windows XP and Office 2003 are in their "Extended" support phase, which ends in 2014. Once this hits, they'll cease receiving even security updates, leaving anyone still running that software open to whatever malware the Internet throws upon them. Windows Vista and Office 2007 will be in Extended support from now until April 2017.