In many of the tweaks around and about VistaBase, you sometimes need to delete or replace a system file. In Windows Vista this is not always as easy as it sounds since the system files are protected better by the file system than in XP. There are two steps that you need to do in order to be able to replace or delete a system file:

1. First you need to take ownership of the file. At the Run command (press Windows key + R), type in:
         takeown /f  “path and file name”     to take ownership from a command prompt.
2. Next, you need to give your account full control permissions on the file. Run from the same command prompt:
         cacls “path and file name” /G <your username>:F     to get full control from a command prompt.

Source: TweakVista