Actually there are more than 3 types of users in XP:
Administrators
Backup Operators
Guests
HelpServicesGroup
Network Configuration Operators
Power Users
Replicator
Remote Desktop Users
Users
For a detailed explanation on all these go here:
http://www.microsoft.com/technet/tre...d_sec_ikgy.asp
or if you don't want to put into Safe Mode to get the security panel
Go to My Computer, Tools, Folder Options, View Tab
At the bottom, uncheck "Use simple file sharing" and you now have the security tab.