This is more of a html question than hibernate.
First you query the database for the string/id combinations. These you use to populate the selectbox, using the string as display value and the id as value.
How to do this is dependent on the framework you use, but should result in somethnig like this in your page:
Code:
<select id="form-element-id">
<option value="121">Volvo</option>
<option value="243">Saab</option>
<option value="32">Mercedes</option>
<option value="373">Audi</option>
</select>
When the form is submitted the selected value (id of the string) is available in the form-element-id variable.