All XP machines have an
uber user (the equivalent of UNIX/Linux root user) who is created automatically on installation. This
uber user is called Administrator, which is confusing, since by default ordinary users on XP have the same full administrative rights.
Administrator does not appear on the normal logon screen, only in safe mode (as you have discovered).
If you have full administrative rights you can delete any other user,
except Administrator (who always has full control and can of course delete anyone else).
In many XP installs Administrator doesn't have a password - you might think this a huge security hole, but XP does not allow anyone on the network to logon as Administrator if the password is blank, so it isn't THAT bad.
Non-Administrator users (User, Power User etc.) in XP have limited rights which is a GOOD THING - it means that they (and programs that they run) can't stuff up the system. Unfortunately in Windows a lot of programs won't run properly if they are started by a user who doesn't have full administrative rights, so XP
by default gives all users full Administrator rights!
Daft innit! That's why Windows is so vulnerable to hackers and viruses.
In a REAL operating system like UNIX/Linux ordinary users ALWAYS have limited administrative rights which prevents them (and malware!) from doing too much damage. It is possible to login as "root" if you know the password and gain full administrative rights but this is only necessary for serious surgery and one should never do it routinely.
NB: It IS possible to change the name of the
uber user in Windows to something else (Jim or Fred or whatever) - this is a
good idea since hackers look for the Administrator account to wreak mischief.