I'm impressed with Greg's craftsmanship which you can see in the photos below, but what you can't see is that he used an Arduino to program the ATTiny85 with the original code which can be found here. This is cool because if you have an Arduino laying around, but no programmer, you can still make a modulating LED brake light for yourself. Greg said the following links were useful to him in using his Arduino as a programmer http://hlt.media.mit.edu/?p=1229 and http://hlt.media.mit.edu/?p=1695 but ended up not changing the default 1 Mhz clock on the ATTiny85 and instead changed the delay between flashes in the code from 25 mS to 75 milliseconds.
Have a look at video and pics below to see for yourself how cool Greg's flashing LED brake light turned out. I really like the pattern the LED's make on the tail light lens. If you have any pictures or video of a project you have made with the help of Pete's blog, send me an email, I'd like to see!