This is simple example of uses Ajax to load
a plain text file.
An initial text file, initial.txt, stored on a server using a javascript body onload.
Clicking the button loads a new text file, newtext.txt
Once the file is loaded it is embedded in the page using innerHTML.
You should study the code carefully to become familiar with this new technique.
To find out more search for the term 'ajax xml' on the web.