BYTE -- It's easy to encrypt a Word 2007 doc with a simple key combo. Hold down [ALT] and the type the keys [F] [E] and [E] in that order. Enter a password and make it robust. Write it down so you don't forget it.
The encryption program isn't bullet-proof. There are plenty of Word-cracking programs out there targeting it. But at least you'll keep the regular folk -- and your kids --from accessing your document.
To remove this encryption, just repeat the process with a blank password.