Ajax :: Show Or Hide DIVs In A Large Registration Form

I am building a large registration form. In this form, a sponsor/educator must register himself or herself and then may add up to 6 more " delegates" in pairs. The first two pairs registration info on the form is shown by default. I need to hide the other two pairs until when/if the user clicks on a button to add two more delegates at a time. I used javascript to show or hide the parts of the form that I had put into two divs and adjusted the css display attribute. However, my problem was that, if the user filled out the sponsor/educator section and the first two delegates, and then decided to add two more, when the user clicked on the button to show the part of the form for delegates 3 and 4, it reset all the previous visible form fields to empty. Not good. So, I thought, maybe AJAX.

I created the request object (I am a relative novice at AJAX), had it grab a text file with the code to insert into my target div, in this case a div with id = "delegate3and4". Surprisingly however, it still reset the previous form fields to empty. Am I misunderstanding how AJAX is supposed to work? I figured that, because it does not refresh the page that this would not happen. In fact, to test this out, I created a simple page from scratch with just a single input field and then used AJAX to insert the file in a div after this field and it did not reset the previous input. So, I am totally confused about why this would be happening on my live page. The page is a php page as it submits the form to a php script for processing but I don't think this should make a difference.