OS 10.4 - extensions added in Safari

I know the rote answer is just change it, but my problem is that it's on my bosses computer who is not going to do that! He is terrified of his computer and will not begin to understand that. The strange the is that the other computers with the same Safari & op don't do this so it can't be a server problem. I just want to cause Safari to download the file as it is without adding extensions. I hope someone can help. Thanks in advance.