Se non ho capito male:
codice:
<form method="post" action="pagina.asp">
<%
set conn = server.createObject("ADODB.Connection")
conn.open "Provider=Microsoft.Jet.OLEDB.4.0; Data Source=" & server.mapPath("tuo_database.mdb")
sql = "SELECT * FROM offerte ORDER BY idconvenzionato"
set rs = conn.execute(sql)
if not rs.eof then
%>
<select name="oggetto">
<option value="0">SELEZIONA</option>
<%
do until rs.eof
%>
<option value="<%=rs("IDOfferta")%>"><%=rs("idconvenzionato")%></option>
<%
rs.moveNext
loop
%>
</select>
<%
end if
rs.close
set rs = nothing
conn.close
set conn = nothing
%>
<input type="submit" value="VAI">
</form>