Joe from Telerik asked me to follow up on this post. I successfully implemented PayPal on my site by using the Products Module, making the buttons on PayPal, using their cart and their checkout. Here is how I did it:
1. I created the Products Module
and I added a few products to it.
2. I created a PayPal Premier account and signed up for Website Payment Standard
3. When you login to your PayPal account, click on Merchant Services > Add to Cart
4. Complete the form and on the next page, save the code for the button
5. Add that code to the product that you made in the products module
Everything in PayPal communicates via query strings, so you can also add custom headers and footers to the PayPal shopping cart and checkout by adjusting those links. Here's an article for more info on that
Let me know if you have any PayPal questions.