Normally in XP Pro, through the Control Panel / User Accounts icon, you are only allowed to create administrators or limited users.
If you want to create

   1. Right click on My Computer
   2. Manage
   3. Local Users and Groups
   4. Users
   5. Right click on the user you want to change
   6. Properties
   7. Member of tab
   8. Add button
   9. Advanced button
  10. Find Now button
  11. From here you see the full list of possibilities (e.g. Power User, Backup Operator etc.)