I had a problem like that a year or two ago. Can't remember fully how I did it. Try this: Cancel the file from the download window. Go to Library window, select incomplete folder & press Explore button. Now Close LW. Find that file & send to Trash & empty using Secure Empty Trash. If still not working, reboot into Safe boot mode & do the same thing. Mac OS X 10.2-5: How to start in Safe Mode

3rd option: Find your installation Disk, boot up from it. Find the file & trash it.

Another thought is whilst in safe mode, create a document of same name & put the zip extension on it or zip it. Drag & drop this file into the folder where the bad file is & choose to replace it. This may or may not allow you to do this.

BTW what is the file size? I cannot remember what it was, though I may have posted on the forums about it in past.