Yes, this should work. The AirPort Express Base Station (AX) would not get a Public IP address, but it would have a Private IP address of 10.0.1.1 ... and it would be providing wireless clients, including the WD My Book Live, connected to it with Private IP addresses in the 10.0.1.2 - 10.0.1.200 range.
AirPort Utility > Select the AX > Manual Setup > AirPort > Wireless
- Wireless Mode: Create a wireless network
- Wireless Network Name: <enter a desired Network Name or SSID>
- Radio Mode: <leave the default or select a desired radio mode>
- Channel: Automatic
- Wireless Security: <select the desired wireless security type>
Internet > Internet Connection
- Connect Using: Ethernet
- Connection Sharing: Distribute a range of IP addresses
Internet > TCP/IP
- Configure IPv4: Manually
- IP Address: 10.0.1.1
- Subnet Mask: 255.255.255.0
- Router Address: 10.0.1.1
- DNS Server(s): <leave blank>
- Domain Name: <leave blank>
Internet > DHCP
- DHCP Beginning Address: <leave default or change to a desired starting address>
- DHCP Ending Address: <leave default or change to a desired ending address>
- Enable AirTunes (checked>
- iTunes Speaker Name: <leave default or enter a desired speaker name>
Advanced > Logging & Statistics
- Allow SNMP (unchecked)
Your AX will still report at least three errors: 1) Configuration of WAN, 2) SNMP over WAN, and 3) Double NAT. These can all be safely ignored to stop the AX's status light from flashing amber in this configuration.
Sorry to resurrect an old thread, but I'm after doing the same thing and I'm struggling. I get setting the Airport Express up like this, but my problem is that as I subscribe to itunes match, for some reason my iphone tries to play every song over the internet, rather than accessing from the Mybook live.
What am I doing wrong?