Building a PowerPC Linux Box?

jglassco asks: "Building an Intel Linux box is trivial, but what about building a PowerPC based Linux box? I have searched the /. archives yet have found nothing on this topic. My purpose here is to find sources for the two components that seem the hardest to locate, namely: a motherboard (2 or 4 processors) with 4x AGP slot, and processors. I want to build the rest using the common components found as commodities. Is anyone experienced with this?"