it is very simple
for this u shud ve folder in NTFS drive. (say e:)
once it is done open run->cmdfor locking the folder
cacls e:\(name of the folder in drive f) /d everyone
for unlocking type
cacls e:\(name of the folder in drive f) /g everyone:f
once u hav locked a folder and if anyone tries opening it a message access is denied will be displayed. u dont hav to hide a folder after doing this.