BTW, I think that "move the arduino core" to a new CPU is a particularly GOOD "learning project." However, it requires that you have a background in both the source (AVR) and target (???) CPUs, as well as a basic understanding of what the code you are porting is supposed to do.
For example, I have been (rather sporadically) blogging about my experiences and observations porting the Arduino environment to TI's MSP430 here: http://www.element-14.com/community/people/WestfW/blog