f you've heard about this Arduino thing, but are unsure about where to begin, Getting Started with Arduino is a great book to begin with. 110 pages of easy to read, well written, Make/O'Reilly goodness. Massimo Banzi (author and one of the 5 Arduino developers) describes the basic hardware, writes some simple programs, and explains how to use the free Arduino development environment. The second edition is updated for Arduino !