I just want to echo SamuraiCrow's comments... anybody designing a desktop system not using an x86-64 based architecture is throwing money into a black pit of nothingness... PPC is dead dead dead... forget about it.
If I was to start a project now... I would probably use an ARM chip, the new Cortex designs are nice and fast and are really low power... but only if I was targeting something more specific than a desktop...
