Jeg fandt denne under
http://www.phoenixv.dk/arkiv.html:<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>Dynamisk select-boks</title>
<script type="text/javascript">
valg = new Array("Albatros", "Anders", "And", "Asger", "Bi", "Blomst", "Benjamin", "Bølle", "Citron", "Cykel", "Flæskestej");
valg.sort();
function opdater(felt) {
selOpts = felt.form.sel.options;
selOpts.length = 0;
for (i = 0; i < valg.length; i++)
if (felt.value == "" || valg[i].toLowerCase().indexOf(felt.value.toLowerCase()) == 0)
selOpts[selOpts.length] = new Option(valg[i], valg[i]);
}
</script>
</head>
<body onLoad="document.frm.sFelt.focus();">
<h2>Dynamisk select-boks</h2>
<form name="frm">
<input type="text" name="sFelt" onKeyUp="opdater(this);" style="width: 150px;" /><br />
<select multiple="multiple" size="8" name="sel" style="width: 150px;">
<script type="text/javascript">
for (i = 0; i < valg.length; i++)
document.write('<option value="' + valg[i] + '">' + valg[i] + '</option>');
</script>
</select><br /><br />
<input type="submit" value="Send" />
</form>
</body>
</html>