Your form should be based on the sample xml script they gave you. The form will need to gather all the required values that are needed by the script.
You can then use the references to these fields in your script to process the transaction. For the PCI compliance you will need to check with vendors that offer this type of certification. Here is a link to the PCI site that gives all the information and details you should need:
www.pcisecuritystandards.org/