Microsoft Releases – WannaCry Patch For Unsupported Windows.

XP Patch can be found here
Windows XP Patch

Windows 2003 Server found here
Windows 2003 Patch

Microsoft Update Catalog – Listed Operating Systems.
Microsoft Update Catalog

Our understanding is that, this patches the vunerability that allows the spread of the infection once launched inside the network.
Your vigialnce is still required however, as more variations, of this and other ransomware are still out there.