Fork from http://sourceforge.net/projects/ard-core13/ (http://forum.arduino.cc/index.php/topic,89781.0.html)
Includes some compilation errors fixes.
Copy attiny13 directory into /Applications/Arduino.app/Contents/Java/hardware/
Copy attiny13 directory into C:\arduino\arduino-<version>\hardware\
Default ArduinoISP sketch too fast for attiny13 @ 128 or 600 KHz ("Invalid device signature" error). To fix that, in ArduinoISP sketch change string:
#define SPI_CLOCK (1000000/6)
with:
#define SPI_CLOCK (128000/6)