This guide applies, it seems, to liquid-cooled CPU G5s, which are rather rarity IMO.

Air-cooled G5s are completly different kettle of fish, and they come in two flavours as far as CPUs brackets (those studs on which CPUs are attached to the aluminum case) are concerned. One uses phillips screws and some guiding rods (AFAIR) - plain and simple solution, while the other uses allen bolts and sort of "expanding" studs, which have tendency to get stuck, PERMANENTLY, to the CPU's base plate. Which means, in turn, that you can easily tear them completelly off their sockets (weak and shallow ones) while attempting to lift the CPU.

Besides, the whole thing (getting the MB out) is exercise in high dexterity and saintly patience thanks to Apple's decision to save few cents on machines costing thousands of $ by making all wires shorter than necessary for easy dismantling, by an inch. Bunch of smart-!@# morons, if you'd ask me... and this is not the only issue with these machines (which are otherwise great computers).