Windows VirtIO Drivers
The source for the Windows drivers is hosted in a repository on GIT hub. Anonymous users can clone the repository
git clone git://github.com/YanVugenfirer/kvm-guest-drivers-windows.git
Binary drivers are provided by some Linux distributions including WHQL Certified drivers.
For example the binary drivers for Ubuntu can be found here.
64-bit versions of Windows Vista and newer (this currently includes Windows Server 2008, Windows 7, Windows 8, Windows Server 2008 R2 and Windows Server 2012) require the drivers to be digitally signed to load.
If your distribution does not provide binary drivers for Windows, you can use the package from the Fedora Project. These drivers are digitally signed, and will work on 64-bit versions of Windows: