De nuevo, la ruta ya la sabés porque sos vos el que se la indica:
Código:
<SELECT name="Imagen">
<%
RutaIndicadaPorMi = "/imagenes/"
Set fso = CreateObject("Scripting.FileSystemObject")
Set folder = fso.GetFolder(Server.Mappath(RutaIndicadaPorMi))
Set files = folder.Files
For Each file in Files
%>
<option><%=RutaIndicadaPorMi & file.Name%></option>
<%
Next
Set files = Nothing
Set folder = Nothing
Set fso = Nothing
%>
</SELECT>