Microsoft WannaCrypt Hotfix Patch can patch Windows XP, and Windows Server 2003 against the Wannacrypt ransomware as well as anyone who isn't using Windows Updates.
Customers who are running supported versions of the operating system (Windows Vista, Windows Server 2008, Windows 7, Windows Server 2008 R2, Windows 8.1, Windows Server 2012, Windows 10, Windows Server 2012 R2, Windows Server 2016) will have received the security update MS17-010 in March.
If customers have automatic updates enabled or have installed the update, they are protected. For other customers, Microsoft encourages them to install the update as soon as possible.
Because of this, we have provided direct links to the update for those running XP and 2003 Server.
Windows Vista, 7, 8, and 10 users should be patched. Check your windows updates. As long as the last check was done between late March and now, you're fine. Otherwise, follow the "Windows Vista, 7, 8, 10" link to find the right patch at Microsoft.