Works amazingly. truecrypt.org/ It can define an encrypted simulated drive on your HDD, protected by password or key file (store on USB disk or so). Or encrypt whole partitions.
And create a hidden second encrypted drive within the first one. Really hidden among arbitrary data filling in the empty parts of the outer encrypted drive. Kind idea your wife or the NSA forces you to reveal the password to the encrypted drive E:. But all they find is a collection of “why Mr. Spocks loves Kirk” novels and a few Orion slavegirls pics.
The real important data, like your diary describing your adultery affairs or your secrets as an agent working for the Austrian Navy Intelligence are within a second drive X:\ nobody can see.
Ecrypts USB drives also. Much better than commerical software we made in my old security company 
%*& // that is “Bob” in encryption