It worked for me hope it works for you too.
1) If you want to lock a folder named pocket in your C:\, whose path is C:\pocket
2) Now open the Notepad and type the following
ren pocket pocket.{21EC2020-3AEA-1069-A2DD-08002B30309D}
3) Where dark is your folder name. Save the text file as loc.bat in the same drive.
4) Open another new notepad text file and type the following
ren pocket.{21EC2020-3AEA-1069-A2DD-08002B30309D} pocket
5) Save the text file as key.bat in the same drive.
6) To lock the pocket folder, simply click the loc.bat and it will transform into control panel icon which is inaccessible.
7) To unlock the folder click the key.bat file. Thus the folder will be unlocked and the contents are accessible.
I found a video in Metacafe site:
Windows XP Secrets #1- Lock Folder Using Notepad – The funniest videos are a click away