Hiding existing windows 7 and loading decoy windows 7 instead

I have windows 7 64bit installed on my computer (NTFS).
I wish to hide this installation and create a "decoy" windows 7:

When the computer boots up, it will boot to this new "decoy" win 7.
If, on the other hand, when the computer boot up, I will insert a USB driver with a loader - it will load up a password screen in which after writing the correct one it will open the existing, hidden win 7.

I looked at DiskCryptor but I was only able to password protect the default OS.
Is it possible to do such thing?

Thanks!

 

This is exactly what a modified install of the TrueCrypt Hidden OS will do. Search around.

 

What is the benefit of all this hassle n decoys?