After 12 years, support for Windows XP and Office 2003 ended April 8, 2014. There will be no more security updates or technical support for the Windows XP operating system.
This effectively means that XP will slowly become unsecured, and incompatible with new hardware. It is very important that customers migrate to a modern operating system such as Windows 8.1.
Customers moving to a modern operating system will benefit from dramatically enhanced security, broader device choice for a mobile workforce, higher user productivity, and a lower total cost of ownership.
Office 365 does not have an operating system requirement. Office 365 will not block users from connecting to the service from Windows XP devices after April 8, 2014.
However, it is recommend to upgrade to a modern Operating System such as Windows 7 or Windows 8.1. to avoid any connection issues to Office 365 services.
For more information you can contact our support department or refer to Microsoft FAQ.