How to hide Credit Card Payment Method on Magento with Onepage Checkout enable?

How to hide Credit Card Payment Method on Magento with Onepage Checkout
enable?

I want to keep Onepage Checkout enable (YES), but just one to offer the
standar on Paypal site payment. By default once Onepage Checkout is
activated, Payment page will show the Credit Card option. My question is:
How to hide the Credit Card Payment Option even with Onepage Checkout
enable, just to offer Paypal site payment (standar) ?? My engine is
Magento 1.7.0.2. Please let me know files and codes to change. Thanks in
advance. Hergonof