This post is a summary that covers how to turn your arduino board into an ISP programmer and use it to program an ATtiny85 or 45 8-pin microcontroller.
The instructions in this post are based on the following two tutorials written by David Mellis:
Arduino board as ATtiny programmer >> http://hlt.media.mit.edu/?p=1706
Programming an ATtiny w/ Arduino 1.0.1 >> http://hlt.media.mit.edu/?p=1695
If you get fed up with all the wires, see how to make your own ATtiny programming shield for Arduino: