Collection of links:

• Prosa about programmable thermostats: http://www.oeko.de/oekodoc/1594/2012-450-de.pdf
• Controlling thermostats via Ethernet, powered via PoE: https://www.arduino.cc/en/uploads/Main/PoE-datasheet.pdf
• Network interface with microcontroller (From Elektor): http://www.rs-online.com/designspark/electronics/blog/networker---an-advanced-web-server-with-a-microcrontroller
• PoE Injector: http://www.elv.ch/Der-Ethernet-Injector-PoE-I-%E2%80%93-Power-over-Ethernet-Einspeisung/x.aspx/cid_726/detail_40470
• PoE DP: http://www.elv.ch/Power-over-Ethernet-Splitter-PoE-S/x.aspx/cid_726/detail_39662