Drupal 7 - Ajax form in modal window I try to create modal window with form (from page /node/add/page).
Try this

hook_menu() {items['mypath']=...} + callback (where echo drupal_render($form); exit();)


//form has many elements from different modules (node + inline register)

Next


get rendered form via ajax (form has action 'mypath')
plug jquery.form.js to the form


Submit

Server returns full page and i'm sure that new page material doesn't save even if i change action to '/node/add/page' instead of 'mypath'

What i do wrong?
It's hard to tell what you doing from your description. A better description could possibly yield better answers.

One possible problem could be that the form needs to be loaded on the page the it is submitted on. This is required for the validate and submit handlers to be processed.