Are you wanting the php script to record each time it is downloaded AND report how many times that is? Or are you wanting the script to use your webhosts logs to report how many times it has been downloaded?
The best way is to mimic the download process, and load in the file using the header function in PHP. I wrote a little script for someone else on TalkPHP like this not so long ago, but I was unable to find it with a quick search a moment ago. But that way you can then put all the PHP into the download process, so you know when the user is presented with the download prompt, that you can increment the download count, too.
The man who comes back through the Door in the Wall will never be quite the same as the man who went out.