Microsoft will end all support for Windows XP on April 8, 2014.
Office 365 will not block connections from fully patched Windows XP computers after April 8, 2014, but connectivity to the service will be at risk. Windows XP workstations that have not deployed all service packs and automatic updates run an even higher risk of Office 365 connectivity issues after support for Windows XP ends.
Microsoft strongly recommends that you upgrade your Windows XP workstations to Windows 8 or Windows 7 prior to April 8, 2014.