Java, PHP or what?

Hi, My boss told me to start thinking about an application that works embeded into a browser. First, I thought about PHP because I have some experience after developing some e-commerce sites with that great language, but later I saw some problems with that. I need "real" time interactivity between the application and the user, just like a normal application does. I also need something as a DB grid component used in RAD tools. The think is to get an application into a browser more than a simple html page with JavaScript all around. The big questiuon is : what language/tool will you use to develop an application that kind? Java ? Are PHP+Javascript powerful enough ? Thanks in advance. Xavi.