IF you google this, there are some third part tools (not free though) that will do the trick for you.
I personally use Windows XP's (presuming you are using XP) built-in Permissions feature.
To use this, you will need to password protect your account and, if in XP Home edition, boot into 'Safe Mode'
From there you simply right-click a folder or file and click the 'Permissions' tab. Change it to suit your needs
If you have XP Pro, you can do this in 'Normal Mode'