Javascript is not Java, Javascript is a part of browsers and you don't need anything, if you want to use Java you must to install Java Virtual Machine, i think.
I see that you are using PHP in your that script, that's the good thing. Forget about javascript and use just PHP to do that. I can tell you something about certains bugs in your...
In Mozilla based browser in IE 7.0 as well you cannot to perform cross domain request using AJAX, so it seems that iframe is the only chance for you :)
Hello, PHP is very easy to learn, i think if you are ASP experienced developer, it will be much easier for your. The big advantage of PHP is the simplicity and great PHP manual. Though i didn't buy...
This depends on user's OS settings, if user has associated video file for example mpg with e.g. Quicktime player, video file is automatically played in the browser when user clicks the link.