with paypal standard, all that needs to be changed is the forms action:
<form name="checkout_PP_LI_Hid" action="https://www.sandbox.PayPal.com/cgi-bin/webscr" method="post">
to:
<form name="checkout_PP_LI_Hid" action="https://www.PayPal.com/cgi-bin/webscr" method="post">