A while back I linked to a demo of a script I wrote implementing the unix command tail (Like for watching the data being appended to a file), so I could tail a log file. I finally got around to posting the source code.
You’ll need saja the secure ajax for PHP framework and my saja.functions.php file as well as the actual output page, tail.php.
As with most of my code its icky and hackish, but it works. For me at least.