add 3 field form to checkout page of My Big Commerce site

We need to add 3 fields to the checkout process on a My Big Commerce shopping cart. The submitted data can be stored in a database, emailed, both, or recorded another way you know of. The three fields are: A text box A date selector or even better a calendar to select date of delivery A radio button to select AM or PM delivery time We have already found the file you need to edit to put a form on the checkout page ([login to view URL]) however we do not want an extra submit button, we would like the form to submit when you click the continue button already built into the shopping cart. Please find a link to the site in question in the attachment. I was placing the form on step 5 of the checkout but you can put it somewhere else as long as it is not a step like step 2 because that step will be bypassed by existing customers. Note: My Big Commerce is the web based version of Interpsire shopping cart. If you didn't already know this, then you are probably not the right candidate.