Customizing the "Add to Cart" button to point to checkout

Hey there,

I'm interested in customizing the Add to Cart / Buy now button so it points to the checkout area once a customer selects an item.

How can I begin to achieve this?

For example:

1. Customer clicks the "Add to Cart" button.
2. Button transforms into "Checkout" button, which sends customer to the checkout area when clicked ... perhaps changing color as well, much like Storenvy's button.