I want a button that zoom in (increase font size is the main objective but images and tables etc is also wanted)
There is the zoom css3 property which does exactly this, the latest webkit browsers (chrome, safari) support it.
edit: apparently even IE6 supports it in some way, check comments below
setting the zoom css property on your body or container should to the trick. Could be as simple as $('body').css('zoom', '200%');
with jQuery.
Check http://jsfiddle.net/Ks6Yn/1/ for an example