<Select name=aaa id=aaa onchange="bb.value=value">
<option value="123">123</option>
<option value="456">456</option>
</Select><input id=bb name=bb>
<option value="123">123</option>
<option value="456">456</option>
</Select><input id=bb name=bb>
document.formName.inputName.value=document.formName.selectName.options[document.formName.selectName.selectedIndex].valuedocument.formName.inputName.value=document.formName.selectName.options[document.formName.selectName.selectedIndex].text