Start basic with a robot arm and an Arduino. If you can get it to operate using serial monitor, you can then learn to add Ethernet control.
Look at this list. http://www.instructables.com/pages/search/search.jsp?cx=partner-pub-1783560022203827%3Anpr2q7v5m6t&cof=FORID%3A11&ie=ISO-8859-1&q=arduino+robot+arm