AVR-Chat

Hi all, I want to standardize my inter-chip communication
on the TWI protocol, but I am having no luck whatsoever
finding a working TWI Slave for avr-gcc that uses the
built-in SPI hardware on the ATtiny and ATmegas.

Has anyone attempted this?  Might I beg/borrow/steal
your code :)  I have to admit that the data sheet
gets a little hairy for me when it delves into the
dark underbelly of the SPI's many uses.

My "big idea" is to be able to offload sensor and locomotion
processing on my hobby robots to small, fast, intelligent
periphereals.  I can probably go with SPI or straight
serial, but the hard-headed side of me is becoming
fixated on the lack of a good TWI Slave library for gcc.

Any thoughts, pointers or contributions are welcome!

-Matt
AVR Newbie.