Andaba buscando algo parecido a lo que preguntabas y encontre esto, espero te sea de utilidad:
<HTML>
<BODY>
<FORM
NAME="myForm"
>
Select here :
<SELECT
name="myCombo"
onChange="
this.form.editable.value =
this.options[ this.selectedIndex ].text;
"
style="
position:absolute;
top:10px;
left:10px;
z-index:-1;
width:100px;
clip:rect( 0px, 100px, 22px, 80px );
"
>
<OPTION value="One">One
<OPTION value="Two">Two
<OPTION value="Three">Three
</SELECT>
<INPUT
TYPE="text"
NAME="editable"
STYLE="
position:absolute;
top:10px;
left:10px;
z-index:1000;
width:80px;
"
>
<P>
<INPUT
TYPE="submit"
VALUE="Submit"
>
</P>
</FORM>
</BODY>
</HTML> http://www.faqts.com/knowledge_base/view.phtml/aid/8220