Qualcosa del genere?


codice:
<html>


<head>
	<style>
		.fields {
			display: none;
		}
	</style>


	<script type="text/javascript">
		function printResult() {
			var selectedVal = document.forms[0].list.options[document.forms[0].list.selectedIndex].value;
			var fieldGroups = document.getElementsByClassName("fields");


			for (var i = 0; i < fieldGroups.length; i++) {
				fieldGroups[i].style.display = "none";
			}


			document.getElementById("fields" + selectedVal).style.display = "block";
			document.getElementById("showResult").innerText = "Your number is: " + selectedVal;


			return false; //dont submit the form
		}
	</script>
</head>


<body>
	<form action="" onSubmit="return printResult(this);">
		<select name="list" onChange="printResult();">
	    <option value="1">1</option>
	    <option value="2">2</option>
	    <option value="3">3</option>
		</select>


		<div id="fields1" class="fields">
			<input type="text" value="Field 1 of group 1">
			<input type="text" value="Field 2 of group 1">
		</div>


		<div id="fields2" class="fields">
			<input type="text" value="Field 1 of group 2">
			<input type="text" value="Field 2 of group 2">
		</div>


		<div id="fields3" class="fields">
			<input type="text" value="Field 1 of group 3">
			<input type="text" value="Field 2 of group 3">
		</div>




		<input type="submit" value="Submit">
	</form>
	<span id="showResult"></span>
</body>


</html>