eller tilføje en onload ;)
<script type="text/javascript">
pris = 20;
function blomme(e){
b = e.options[e.selectedIndex].value
d = document.getElementById('noget')
d.innerHTML = "ex moms " + (b*pris) + "kr.<br>" + "inc moms " + (b*pris*1.25) + "kr";
}
</script>
<body onload="blomme(document.forms[0].valg);">
<form>
<select name="valg" onchange="blomme(this);">
<option value="1" selected>1</option>
<option value="2">2</option>
<option value="3">3</option>
<option value="4">4</option>
<option value="5">5</option>
<option value="6">6</option>
<option value="7">7</option>
<option value="8">8</option>
<option value="9">8</option>
<option value="10">10</option>
</select>
</form>
<div ID="noget" style="position:absolute;"></div>
</body>
