XP PRO: In Windows Explorer, go to Tools, Folder Options, View and uncheck
Use Simple File Sharing. Now, when you right click on a drive, folder or
file (on an NTFS partition) and select Properties, you'll see a Security
tab. Here you can assign or deny permissions based on user name or user
group membership.
XP Home: To change the permissions on other folders, you need to boot the
computer to Safe Mode and log in on the built in Administrator account. In
this mode, you'll see the Security tab in Properties, and you can assign
permissions based on user name or group membership.
How Do I Get the Security Tab in Properties - XP Home (makes the Security
tab appear outside of Safe Mode)
http://www.dougknox.com, Win XP Tips section