Need a feedback on my Javascript code and app implementation idea
From a quick glance there are a couple of points where your making simple mistakes.

// Document.write is bad
document.write('&lt;script language="javascript" type="text/javascript" &gt;');

// use css definitions instead
counter_div.setAttribute('style', 'width: 310px; height: 50px; font-family:lucida,tahoma,helvetica,arial,sans-serif; display: block; overflow:hide;');

// dont set inner html. This is bad. use DOM manipulation instead
title_span.innerHTML = meter_title;

// uses eval here. pass a function rather then a string
setInterval("increment()", interval);

// forgetting to declare addCommas with `var`. This is implecetly global.
addCommas = function(nStr) {


I shall have a look at how to redesign this. 

Why do you need to append the div after the script tag. It's bad by design to use the script tag in the DOM for positioning.

it would be better to create a &lt;div&gt; to fill with the timer/counter.

Refactored partly here. This includes fixing the issues above plus making the dom manipulation a bit nicer. 

I'm not too certain how to do refactoring on your timer code.