I've just tried out a few freeware encryption programs. The ones I felt were most useful were:
1) TrueCrypt (
http://www.truecrypt.org/ ). Probably more powerful than what you need, it creates a "hidden" virtual drive that can only be accessed by password. The main drawback that I could see is that if you need a large capacity storage area, it would be best to set up a number of smaller drives - as someone could find a suspiciously large file on your machine and suspect that it has your data. They shouldn't be able to access it, though - and the help file gives a way to further obfuscate your data should you be forced to give up your password under threat of violence!
2) AxCrypt (
http://axcrypt.axantum.com/ ). A lot easier to use, just right-click and password protect.