I don't know the answer to your question , at least not in XP :-(

But this might help :-)

Try downloading a File Encryption Program, you can find a lot of pretty secure free distr.s on download.com... It works much like winzip- or winzip also has the ability to lock archives...

for those of you who are on a *nix box, this can be done in the command line... this link might be useful :-)
http://www.jtpfxp.net/dirunix.htm

Hope this helps...

Have a Nice Day!