Create a form Post and redirect in code behind

Hi all
This is my problem: I am creating a Confirm Purchase page, on this purchase page is a button called Pay Now. This button needs to redirect to PayPal where the user completes payment.
For testing I was using the PayPal BuyNow buttons which looks something like this:

<form action="https://www.sandbox.paypal.com/cgi-bin/webscr" method="post"> <input type="hidden" name="cmd" value="_s-xclick"> <input type="hidden" name="hosted_button_id" value="1054169"> <input type="image" src="https://www.sandbox.paypal.com/en_GB/i/btn/btn_buynow_LG.gif" border="0" name="submit" alt="PayPal - The safer, easier way to pay online."> <img alt="" border="0" src="https://www.sandbox.paypal.com/en_GB/i/scr/pixel.gif" width="1" height ...