Well... there's the default form for DPM. Download the PHP SDK, take a look at the file AuthorizeNetDPM.php in the lib folder for the function getCreditCardForm(). But it may not be the best form in the world either. What API (AIM, SIM, DPM, etc.) are you trying to integrate for, and what information do you want to collect? Do you have enough of your web site up so we can take a look at what the rest of it looks like? Stock forms won't necessarily look good against a specific design.