Install
Sun VirtualBox and under it install another OS - it could be Windows or Linux.
This way you will be able to boot your little private Windows under main Windows, have separate login and absolutely no way to peek into activity into this "little" Windows from outer Windows.
I often use this approach within restrictive corporate environments when I don't want to leave any cookies or traces of activity within "main" Windows.
I am not 100% sure though that main keylogger's logging won't be able to intercept keystrokes within sub-windows.
A while ago I created a little program that notifies about any file system activity on disk - so you may use similar approach to detect where and whether keylogger is active and intercepting keystrokes.
Gleb