Here is another solution using Jquery I find it a little easier and neater than inline JS sometimes.
<html>
<head>
<script src="//ajax.googleapis.com/ajax/libs/jquery/1.10.1/jquery.min.js"></script>
<script>
/* if you prefer to functionize and use onclick= rather then the .on bind
function hide_show(){
$(this).hide();
$("#hidden-div").show();
}
*/
$(function(){
$("#chkbtn").on('click',function() {
$(this).hide();
$("#hidden-div").show();
});
});
</script>
<style>
.hidden-div {
display:none
}
</style>
</head>
<body>
<div class="reform">
<form id="reform" action="action.php" method="post" enctype="multipart/form-data">
<input type="hidden" name="type" value="" />
<fieldset>
content here...
</fieldset>
<div class="hidden-div" id="hidden-div">
<fieldset>
more content here that is hidden until the button below is clicked...
</fieldset>
</form>
</div>
<span style="display:block; padding-left:640px; margin-top:10px;"><button id="chkbtn">Check Availability</button></span>
</div>
</body>
</html>