On your Windows DNS box, make sure that you have the correct IP address of your SME box as the gateway.
On your SME box, why do you want it to redirect back to the Windows box? It is sitting between you and the world, it should resolve external address for itself and if your Windows box is correctly configured, the Windows box should resolve External and Internal address on your network. If you change the SME box to be in Server mode, then you will need to configure the correct DNS and Gateway IP Addresses.