The AP Express has only one WAN port - no others. The Extreme has 3 ethernet ports in addition to the WAN port. The Time Capsule is intended as a Time Machine back up volume, although you can probably use it as a NAS as well. The Time Capsule looks to be an AP Extreme with a HD inside. BTW, I scored a new AP Extreme (802.11n) on eBay for $64.99 "Buy it now." I'm using it exclusively for streaming iTunes to my living room stereo - it is not connected to the internet.