You probably want to read the Microsoft documentation on how to lockdown the server extensions (http://www.microsoft.com/technet/treeview/default.asp?url=/TechNet/prodtechnol/sharepnt/maintain/security/stssecur.asp). This link is actually for SharePoint Team Services but almost everything also applies to the FrontPage extensions version 5. The link that Joe-Clifton pointed out refers to Unix versions. The extensions on NT use Windows accounts.
Good Luck, Tom
