Previously in Windows XP the default Administrator that was created had access to every part of the machine and any applications that was executed by that account also had full access to the machine. This meant that if a machine was infected with a virus then that malware could have access to whole entire machine. Equally, It also meant that you as a user could potentially cause damage to your machine since you were not restricted on the files at which you could delete.
Microsoft understood these security flaws and introduced User Account Control into Vista. This separated Administrators into two different groups. Standard Administrators and Elevated Administrators. The first Administrator created which you are currently using is a standard administrator which means that everything that is run or opened in that user only has Standard user permissions. If an application wants to access restricted content such as be able to install itself then a User Account Control prompt appears asking if you want to allow this. This offers many benefits, Firstly, if any virus managed to infect the machine then its ability to access the machine is restricted and when it does try to access restricted content then you would be prompted by UAC. Secondly, it also prevents you from copying, deleting or removing some files or folders since they may cause damage to the machine or the folder is not owned by you. For example another users files.
The system itself needs to use an elevated account in order to complete administrative tasks without prompting you everytime. To complete this the system will use an Elevated Administrator account. This is normally known as 'SYSTEM'. It is possible for you to activate an Elevated Administrator account so that you can use your machine without UAC prompts while other users still receive UAC prompts. To do so simply follow this tutorial -
http://www.vistax64.com/tutorials/67567-administrator-account.html
Warning
Any programs or applications run when logged into this user account will have complete control therefore this account should only be used to complete admin tasks such as copying users files for a backup
As for your ownership problem, Every file or folder has an owner to it who has complete control and any other users cannot access it unless specified. When backing up or accessing other users folders and files you can end up being denied access. If you would like to take ownership of a file or folder then simply follow this tutorial -
http://www.vistax64.com/tutorials/67717-take-ownership-file.html
From that tutorial I would recommend following Option three.
Hope This Helps,
Josh!
