This same thing happened in your previous, nearly identical topic. I get the feeling you want us to write your code for you rather than guide you to find the answers yourself.
There are a lot of things that have to line up perfectly to get AJAX to work, and if you start with an incomplete understanding of how Struts works, you will never get AJAX working.
Again, my advice is to get something working without AJAX, then adapt the program to use it. Start with the basic Struts tutorial I linked above.