Answer: The below drop down box and text field do what you describe. I have only put three "names" in the drop down list with associated values but it should be sufficient to show how the drop down list to text field copy works.
The code to produce this effect follows:
<form name="ex" method="POST"><div class="centre">
<select name="sel" size="1"
onchange="document.ex.selvalue.value = document.ex.sel.options[document.ex.sel.selectedIndex].value;">
<option value="100" selected="selected">full</option>
<input type="text" name="selvalue" size="10" maxlength="10" value="100"
onblur="document.ex.selvalue.value = document.ex.sel.options[document.ex.sel.selectedIndex].value;" />
This article written by Stephen Chapman, Felgall Pty Ltd.