The reason why you cannot delete system file in Vista/Windows 7 is because you do not own those files, even if you are an administrator. By default, it is owned by the TrustedInstaller service. To overcome this problem, all you have to do is change the ownership of the file to your user account. I must say that this is a long process to do. Luckily, a Vista hack has been featured at howtogeek that adds a “Take Ownership” option on the right click menu.
All you need to do is download and install a small registry hack here, and you are good to go! No system restart required.
Having this menu, everytime you right click on a file or folder will give you the option to instantly take ownership of that file/folder that can grant you a full read/write previlidge to it, and force other users to go through the UAC for that particular file.
