Arial font problem

I am having a problem with some Photoshop CS2 documents, and I've narrowed

the problem down to my Arial font. The Photoshop files work fine as long as I

use any other font, but as soon as I try to change some text to the Arial

(regular, non-narrow, non-bold, non-italic) font, I get an error message. The

Adobe support forums suggest that the problem is due to a corrupted font and

they suggest ways to narrow down which font it is.

I've tried deleting the arial.ttf file in C:\Windows\Fonts, but Win XP Pro

won't let me delete it. I've tried installing a new copy of the arial.ttf

file, but it tells me that I must first delete the old copy before trying to

delete a new one.

Obviously there's something special about the Arial font that Windows won't

let me delete it. How can I restore an uncorrupted version of the font so

that hopefully Photoshop will be happy?

Dan