ARDUINO

Download and Install Arduino Environment: http://arduino.cc/en/Main/Software

Reference Library: http://arduino.cc/en/Reference/HomePage

Getting Started Guide: http://arduino.cc/en/Guide/Windows#toc2

XIVELY

Get Arduino Library: https://github.com/xively/xively_arduino/archive/master.zip

Add Xively library to Arduino software libraries

Set up HTTP Client: https://github.com/amcewen/HttpClient/archive/master.zip

Add HTTP Client to Arduino software libraries

TUTORIAL

Connect Sensors to Xively: https://xively.com/dev/tutorials/arduino_wi-fi/