Try it in Safe Mode. Boot the system, start tapping F8 until the menu
appears, then select Safe Mode and press enter. In Safe Mode, open Windows
Explorer, go to Tools, select Folder Options, go to the View tab, scroll to
"Use Simple File Sharing" at the bottom of the list, remove the check, click
apply and ok. Now you should be able to see a security tab as outlined in
Ronnie Vernon's post.
NOTE: once you boot back to the XP desktop, because this is XP Home, that
tab will not be available but if you need to do this in the future, boot
back to Safe Mode as I have instructed and you can repeat the procedure for
other items if necessary.