JSON on IE6 (IE7)
Since you want to use the JSON.stringify method, you will need to include the JSON3 parser in order to support it on IE < 8.
This library complies with the standard methods of the ECMAScript 5th Edition specification and it checks if there is a native implementation available, so on modern browser this native implementation will be used.
There must be something misunderstood. The object notation has been in JavaScript for a while now (as far as I understand, it's a core concept of JavaScript). I mean, the ability to write code like var o= {a:"b"};
So, if you can do this, you can also call eval('var o= {a:"b"};') and that's the way you "implement JSON" in any browser.
UPDATE: Re-read your post and finally got the point that the problem is serializing objects, not deserializing them. Then you can use the JavaScript library for that: https://github.com/douglascrockford/JSON-js/blob/master/json2.js