Net 30 Days

I have the checkout form that comes with Power store. I would like to add a third option for payment, on account (Net 30) for those that have been granted credit. I have all the dreamweaver extensions, so I am able to modify the form. I just don’t know how to get started.

The issue I am running up against is how to stop the credit card validation when someone selects charge account. Right now I have a radio button that has three option, credit card, pay pal and charge account. But when the form is submitted it is asking for the credit card validation. How can I stop the validation or is their a better way of doing this?

Thank you for your help