AJAX, JSON And Microsoft.XMLHTTP

I am trying to use AJAX and JSON to do this. I have copied an example of
using HttpRequest Object as the backbone of this from
http://www.w3schools.com/dom/dom_http.asp. Further, I am enclosing both of
my files here, in full as opposed to mere snippets. This code does what I
wish it to do except:

1. It does not update when getdata.php is rewritten. On non MSIE broswers,
it shows when first invoked, but not subsequently.
2. It fails altogether under MSIE (6.026 SP1 || SP2) -- I never get
xmlhttp.readyState==4 under MSIE.

Code: