Vim does not automatically check and update the screen. Even if you would use autoread and/or checktime you still have to manually activate them and tell vim to load the cahnged file (if it has changed).
Have a look here: http://firstname.lastname@example.org/msg05900.html
You do have to realize that if you made changes to the file, they will be lost once you refresh the page!
Although I don't know why you need this functionality I do wonder if you are using the correct tool for the job, vim is not meant to monitor files.
Anyway, hope this helps.