I need to develop a custom step between the Magento product detail page and the shopping cart. If the user clicks on 'Add to cart' the user should be redirected to a new custom form page to enter his/her birthday first. After submitting the birthday data the product should be added to the shopping cart as normal. The birthday data fields should be saved in the quote- and if the user goes to checkout also in the order-model.
I'm new to Magento development so it would be great if somebody could give me some rough hints or guideline where to start and how to plug in.
Thanks a lot in advance!