<input name=text1 value="a">
<select onchange="document.getElementById('text1').value=this.value">
<option value="a">a</option>
<option value="b">b</option>
<option value="c">c</option>
</select>
<select onchange="document.getElementById('text1').value=this.value">
<option value="a">a</option>
<option value="b">b</option>
<option value="c">c</option>
</select>
<select onchange="getText(this)">
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
<option value="4">4</option>
</select><script>
function getText(obj)
{
document.getElementById("mytxt").value = obj.value;
}
</script>
function changeValue()
{
var str=document.form;
str.text.value=str.select.value;
}
</script>
<html>
<body>
<form name='form' action='' method='post'>
<select name='select' onchange='changeValue()'>
<option value='value1'>value1</option>
<option value='value2'>value2</option>
<option value='value3'>value3</option>
<option value='value4'>value4</option>
</select>
<input type='text' name='text'>
</form>
</body>
</html>