IndigoHollow,
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<script type="text/javascript">
window.onload = function () {
var b = document.querySelector("select"),
c = document.querySelectorAll("div");
b.onchange = function () {
for (var b = this.value - 1, a = 0; a < c.length; a++) c[a].style.display = a != b ? "none" : "block"
}
};
</script>
<title></title>
</head>
<body>
<select name="menu" size="1">
<option name="type" value="0" id="selecter1" select="selected">
</option>
<option name="type" value="1" id="selecter2">
Фундамент
</option>
<option name="type" value="2" id="selecter3">
Перекрытия 1-го этажа
</option>
</select>
<div id="block1" style="display:none;">
БЛОК 1
</div>
<div id="block2" style="display:none;">
БЛОК 2
</div>
</body>
</html>