how can I disable everything inside a form using javascript/jquery?

This is quite simple in plain JavaScript and will work efficiently in all browsers that support read-only form inputs (which is pretty much all browsers released in the last decade):

var form = document.getElementById("your_form_id");
var elements = form.elements;
for (var i = 0, len = elements.length; i < len; ++i) {
    elements[i].readOnly = true;
}