use "enter" to move between form fields

I am trying to get a checkout page set to use a card swipe machine for use at a seminar. The form fields populate from the onSwipe javascript ... the focus text box accepts the swiped info and populates the fields using the "enter" key to move from one text box to another.

My problem ... the enter key causes the entire form to post and go on to the next page. How do I change the form so that the form will not execute until the "checkout" button is pushed. I currently have the trigger for the checkout process set to only activate when the button is pushed, but it still activates when enter is pressed. Hmmm...

I have attached the code. THANKS! I can't find the "how to" for this in any online help section.