Windows VirtIO Drivers
The source for the Windows drivers is in a git repository on kernel.org
Binary drivers are provided by some Linux distributions including WHQL Certified drivers.
64-bit versions of Windows Vista and newer (this currently includes Windows Server 2008, Windows 7 and Windows Server 2008 R2) 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:
Note: as of this writing (2011-Nov-08), latest drivers are of version "15", dated "15-Jun-2011", with the CD image being virtio-win-0.1-mm34.iso. In that image, WindowsXP drivers does not seem to work, it is impossible to install them using regular winXP driver interface. But the previous drivers, version "14" as found on this Directory, dated "13-Jan-2011", from CD image named "virtio-win-1.1.16.iso", installs on winXP fine.