Hi,
You have to combine a edit-field where customers can enter new values, and a
list-field with the existing values from the database.
When the page gets submitted, you just query if the submitted value in the
edit-field already exists in the db-table and use the PK for that value, or add
it to the db-table and find the PK for your new value.

cheers,
fober

===== EXAMPLE =====

<div style="width:200px; padding-right: 20px; border: 1px solid red">
<select id="text_select" size="5"

onchange="document.getElementById('text_edit').value=this[this.selectedIndex].
text; this.style.display= 'none'"
style="display:none; z-index:99; position:absolute; width:100%"
>
<option>Apple</option>
<option>Orange</option>
<option>Banana</option>
</select>
<input name="xyz" id="text_edit" type="Text" style="width:100%">
<input type="Button" value="\/"
onclick="document.getElementById('text_select').style.displ ay= 'inline'"
style="position:absolute; float:right;"
>
</div>