I protect my directories with important stuff in them with encryption. I bought Norton For Your Eyes Only (~$50) about 2 years ago and it works great. When you boot your computer, you log on with a username and password. There can be multiple usernames per machine. Then you can encrypt individual files, or set it up to automatically encrypt files when you place them in a directory. You can also grant other users access to the files in those directories, but by default someone who turns the computer on and doesn't know your password will not be able to open files in your directory, and will only be able to see the file names.
There are several freeware programs that implement RSA type encryption (public/private keys) , for example Pretty Good Privacy (PGP), but I don't know if those programs automate the encryption/decryption process.
There are several you can pay for in the $40-$70 range that offer complete solutions; look for them in the utilities section of your favorite computer software store.
The girlfriend has an idea what the PORN folder is on my computer, but she can't prove it! heh heh
{NBK}Beavis
PS. The automatic encryption/decryption process is fast, I don't notice any delay opening files; on a PIII 550 anyway.