This little circuit sits nicely ontop of an Arduino board and lets you quickly plug in an ATtiny chip for programming using the Arduino "language" and IDE to write the code, and the Arduino board as an ISP programmer to upload the code to the tiny chip.
These instructions are also published on our website titled HOW TO GET WHAT YOU WANT
For instructions on how to use Arduino to program ATtinies, please look at the following links. This Instructable will only explain how to build the programming shield.
Arduino as ISP >> http://www.kobakant.at/DIY/?p=3742
Arduino board as ATtiny programmer (by Dave Mellis) >> http://hlt.media.mit.edu/?p=1706
Programming an ATtiny w/ Arduino 1.0.1 (by Dave Mellis) >> http://hlt.media.mit.edu/?p=1695
There is also a really nice Tiny AVR Programmer now available from Sparkfun (designed by Dave Mellis) that does the same thing even more compactly >> https://www.sparkfun.com/products/11460
Video of "ATtiny Arduino Shield Programmer" in action