Not many files are that large...I'm willing to bet it's the only non-video file (video files shouldn't have a defrag problem, so you should be able to rule them out) on your hard drive that's that size. Just go run->search->all files and folders->what size is it?->"specify size (in KB)" and type in 4,000,000. (Make sure that you have enabled the viewing of "hidden" files first by going tools->folder options->view->show hidden files and folders.)
Unfortunately, this is the only method I know of, and it's not very exact. (If you have multiple files that size, you won't be able to pinpoint the right one.) Perhaps someone knows of a program designed for this?
Hope this helps,
I have WinXP Pro SP2 and use Diskeeper 9.0 to defrag. Recently, I've developed a single fragmented file that just isn't going anywhere, and it's huge (~4-5gb). I'm tempted to reformat, but it would be very inconvenient and it's only been a few months since my last reformat. Does anyone know how I would be able to figure out what the file is so that I can get rid of it?