Implementing PayPal Express Checkout (Website Payment Pro)

Project Description:
I have an ecommerce website built on ASP.NET 2.0 / C#
I have already implemented PayPal Website Payment Standard.

Now, i want to replace the Website Payment Standard button with PayPal Express checkout button.

Now, I need an example ASP.NET webform where you use a PayPal express checkout button. Clicking that button will take the buyer to PayPal website and bring the buyer back to my website from PayPal as usual and call API's to finish the payment.

I would learn from your script, how you call APIs to finish the payment from my website using pure C#.NET.

I would need complete examples for following solutions in Express checkout.

1] Subscription button / Recurring Payment
2] Cancel Subscription (where the subscription was made by Express Checkout)

If the payment success, my website should show, success message, otherwise show failure message.