Complex webform, how do i add the amount to the cart?

I have created a new content type called "Donation" and started like this:
http://alturl.com/ege8

Ofcourse, i will add other fields and change the button name from "Save" to "Add to Cart"; but my question is how do i add that amount to the shopping cart? And associate this new node to the order?

I looked at webform to uc (http://drupal.org/node/665190), but not able to install the module.