Using AVR ATmega644P with Arduino IDE

I've seen a couple of projects where the larger, 40-pin AVR chips are used with the Arduino IDE and software framework. One is the Sanguino, and the other is the Duino644:

It looks to me as though the software is based on Arduino version 0018 (whereas the latest is 0022). I'd like to use the latest Arduino code as a basis for working with the ATmega644P. Is there an up-to-date description anywhere that details how to go about this? I think I'll need a new (or modified) 'boards.txt', a new 'pins' file and a new bootloader. Is that correct? Any hints would be very much appreciated!

I did just that for my 1284 based design. Check out the later pages here,61126.0.html to see the kinds of changes needed for -0022.