It seems to be difficult to ajaxify a drupal multistep form(loading next step without page refresh).I googled it but I didn't find any solution. Does anybody know how to do it?
In a recent project I use ctools wizard to get a multi-step form, which I found to be a really good way of making a multi-step form. This wizard also supports using ajax to load the pages.
I found the tutorial here: http://www.nicklewis.org/using-chaos-tools-form-wizard-build-multistep-forms-drupal-6 pretty useful when I was doing it. If you set 'ajax' => TRUE in the $form_info then you should get going.
Use the cache (what they are naming the wombat) to store the results from the various steps as you move through the form and then do something with them at the end.
Ctools link: http://drupal.org/project/ctools