I'd like to recommend a piece of FreeWare that I actually read about here at TechRepublic, and have installed and use: PowerDesk4. It' a Windows Explorer replacement, and including its other convienent functions, it gives you the ability to encrypt either at the folder level *or* at the file level. If you open the folder/file without entering the encryption password, all you get is gobble-de-gook; enter the right encryption password, and all is well. I've found it's a nice little product with alot of functionality (including the encryption tool).
Here's the link to the TechRepublic article where I first read about PowerDesk4: https://www.techrepublic.com/article.jhtml?src=search&id=r00220001214bot01.htm
Here's the link to the download site: khttp://www.ontrack.com/powerdesk/