"Whether you're new to Arduino or a seasoned builder,
this project has something for you. There's nothing quite as
satisfying as creating an interactive physical object, knowing that
if it breaks or needs modification, you know where all the parts go
and how everything works. The 'Duino tag gun is a great project to
work on by yourself or with friends. To complete this project, you
should at least have a basic understanding of electronics (you
should know what a resistor is, but you don't need to know the
science behind one) and have an understanding of programming (you
should know what loops and variables are, but you don't need to be
able to parse Big O Notation). Don't be afraid to jump right
in." Free registration required--ed.