Add a step in checkout

Hello,

In checkout, i want to do this :

Add a step (step 3) for Coupon and Voucher. I Know there is a vqmod for coupon and voucher in step 5 (already installed), but i want it in a step, separatly.

I already add a div in checkout.tpl, and add ajax code, but it is clearly insufficient. Is there someone who knows the "steps" (ajax, tpl, php...) for add a step in checkout ?

Thanks.