versuch dies:
<html>
<head>
<title>Untitled</title>
</head>
<body>
<form name="formular">
<select name="vorname" onchange="document.formular.uebergabe.value = document.formular.vorname.value">
<option value="peter">peter
<option value="susanne">susanne
<option value="rüdiger">rüdiger
</select>
<br> <br>
siehe da: <input type="text" name="uebergabe">
</form>
</body>
</html>