Order Form

hi

I am making a web form in whose name is order.aspx in which user have to add his details .like name contact no etc. but my problem is there are products which i have listed in combo box . if user  select any one item from it it shows its quantity .after selecting he quantity the details of product must be displayed in grid view below .then if user select second product it should do the same grid view must add the second product details to it  and so on.