how to add dynamic form for different product in oscommerece

Question

Below site , doing very good work, its really amazing,

link text

very very nice, very much interactive, no confusion , very easy for stupids also,

see for each product they are having different form in the checkout ,

assume if select product A , if add to cart the product A, then for example they ask enter your helight and textfield , enter your weight ,

Assume if i select the productB , then they as Enter number of adults with text field, Select number of baby seat with combo(drop down)

i like this sort of dynamic form creation , how they doing really, is there any module available ,

otherwise they are hard coding,

if hard coding mean , How they maintain when more packages are coming to desk,

Can you please share your ideas here