How to Password Protect Files on Flash Drives?

I have a 1 gb Victorinox Swiss Army Knife with a built-in flash drive that came with some cheesy program called “Travel and Work,” that doesn’t offer password protection.  I use Windows Vista Basic Edition, so it doesn’t have the ability to password protect files (as far as I know).

Does anyone know how to password protect files on flash drives with a free program, through Vista Basic, or any other way that doesn’t require purchasing a program?