IBM DeveloperWorks recently posted an article titled, “Migrating from x86 to PowerPC: Robots and networked applications”. The article compares the PowerPC (or “Power Architecture” as IBM prefers to call it these days) to traditional Intel x86 and ARM processors. Migrating from one of these architectures to another is actually not too difficult if the software is based on Linux which runs well on all three platforms.
Ultra-cheap methods of getting started with PowerPCs are mentioned, such as cannibalising a Nintendo GameCube console or using a Kuro Box. The author, Lewin A. R. W. Edwards, has published a book with more information on the topic, called A Cookbook for Open-Source Robotics and Process Control.