Ok Let me see if I can expand upon my question...
When you first create a computer, the main user is a default Administrator.
When you create a computer as a workstation for a Network, they are able to log into a Domain. Once in a domain they are given different user acounts: Administrator, Standard, User (these are the main three that they start with when setting up a computer for the network.)
Being part of the Administrator Group, gives you access to everything on the computer. Allowing you to Add, Edit and remove applications to and from your computer.
What I would like to know what groups (for Windows XP Pro) that offer the 'highest security'. That doesn't limit the user to the point where he/she cannot work efficiently on his or her computer.