This program will install windows updates and reboot the machine. By placing it in the startup folder and enabling automatic login, you can take a fresh, un-updated install of Windows - or a stale install for a machine that has been on a shelf for a while - and get it fully updated without having to babysit it and hit "check for updates" after every reboot.
The code is rough and hacky, but should work on Vista, Windows 7, and Windows 8. It is untested on Windows 8.1.
To run update everything, place the executable in the Windows Startup folder, enable automatic login, and disable UAC. Yes, I know this is very dangerous to do. Please only do it long enough to get updated and then turn all of the system security features back on and turn automatic login off. Make sure you remove the application from the startup folder too, or you'll find yourself updating/rebooting suddenly!