I should probably mention that I'm designing a very different kind of case for the G4 mb and would like to run 2 mb's facing each other with a fan blowing from below. No power supply, hard drives, optical drives or anything else will be in the box. It seemed silly to take a whole bunch of heat producing devices and cram them together THEN try to cool them. The optical and hard drives, power supply, DSL and dialup modems, router, voip box, fan controllers, LCD displays for thermo sensors, will all be vertically (for bottom to top air flow) housed in another sound insulated tower with big, slow rpm fans blowing air from the bottom and sucking air out of the top. Should be cool and silent if I've planned correctly. Next thing is EMF screening.