process form in popup window I have a custom module in Drupal and I also have a custom table for storing the details of seminars, such as name, description, date and location.

I am showing the names of the seminars in a left sidebar block; when the user clicks on a seminar name, I want to show its other details (description, location, etc.) in a form (which include a "Submit" button) in a popup modal box.

When the user clicks on the submit button, the user will be joined in the seminar (inserted into database).

How can I use JavaScript/AJAX for this scenario and process form in popup, without refreshing the page?

I have included the jQuery library in my module file using drupal_add_js(); I also installed the Chaos Tools Suite module.
I would suggest you to have a look at Chaos tools suite; the module brings an example for a modal form inside a modal window right with it (AJAX example).
It should be not to hard to integrate that, if you're already working on a custom module.

All I've said is valid for Drupal 6; I haven't looked into cTools in Drupal 7.