Write node in several tabs/step

Hello,

After my project http://www.balado.fr, i work with new project.
I would like to write node and theirs fields in several tabs.
I use tabs module of course, i set "enable" buttons navigation in tabs module, and i have "next" and "previous" in the edit form.
So, i have 2 questions :
- Is it possible to place them at the top of fields in the tab, instead of at the bottom ?
- I would like that user have to write fields in tab 1 before go to tab 2, is there an existing module for this, or have you an idea to do this ?
Or, user could create a node with severals step. He write fields in step 1, valid, an pass to step 2, with anothers fields, ... (one validation by step)
In this case, tabs module is'nt necessary perhaps, because i remind a module whose do this, but i lost this name.

Thank you for your help.