Stubourn files of this type are often found to be associated with some type of Malware or Virus as the so called 'Owners' pathetically try to prevent removal, they can also be actual windows files also.
The problem arises because the associated program, utility, or Malware is allowed to take ownership of the file as the computer boots up, once this happens you will always get the familair 'Denied Access' tag when you try and delete them.
Happy days though someone has devised a simple method to get around this without resorting to registry hacks.
http://www.softwarepatch.com/software/moveonboot.html
Download MOVE ON BOOT and follow the instructions,there is also a small tutorial that explains how it works and why these files are so problematic, the program will allow the files to be relocated at BOOT so preventing the associated program from locating and protecting them, from there they can easily be deleted.