Ett litet DOM-exempel;
<form>
<select name="foo" onChange="if(document.getElementById){for(var i=0;i<9;i++){document.getElementById('in'+i).style.display=(i<=this.selectedIndex)?'inline':'none';}}">
<option>1</option>
<option>2</option>
<option>3</option>
<option>4</option>
<option>5</option>
<option>6</option>
<option>7</option>
<option>8</option>
<option selected>9</option>
</select><br>
<input type="text" name="foo" id="in0"><br>
<input type="text" name="bar" id="in1"><br>
<input type="text" name="asd" id="in2"><br>
<input type="text" name="qwe" id="in3"><br>
<input type="text" name="rty" id="in4"><br>
<input type="text" name="zxc" id="in5"><br>
<input type="text" name="cvb" id="in6"><br>
<input type="text" name="rty" id="in7"><br>
<input type="text" name="bnm" id="in8"><br>
</form>