I am working on a friend's Dell's desktop PC which has failure in booting up (Windows XP).

Here is where I am stuck:
Using Knoppix LIVEDCD to boot up and access the HDD, I attempt to rename and then replace the corrupted system file but get an error message saying file cannot be deleted. The error message when I attempt to rename and also replace file, states: Could not delete file...

What this looks like to me is that even though I can see the file and even copy it to a USB memory stick, there is no permission to modify/delete it.

Any reason why this is the case and what can I do to overcome this?