If you login with a account that is member of the Administrators group you should have full access, but some folders, files and parts of the registry are protected so the access are still limited even if you logon as an administrator. In that case you can rightclick Windows Explorer and select "Run as administrator". That should give you elevated access, but there are still some system files that are protected. This feature is called "User Access Control" (often referred to as UAC) and was first introduced in Windows Vista. You can also disable UAC in the control panel, but that's not recommend since it's mean't as a extra layer of protection to prevent damage to your system by harmful software. With UAC enabled it's harder for software to make changes to your system without your approval.
The same would be the case for other programs so if you for example want to make changes to registry some parts of the registry you won't have access until you start regedit with a rightclick and select "run as administrator". You would have to do this with every program where you want the program to have elevated access to your system.
-gan
