OK, I'll leave deciphering Hervé's post to somebody else
I wonder why no one puts peltier cooling elements in PCs/Macs instead of fans. Peltier elements are way more effective, they can cool the processor down to below room temperature even without addidtional cooling (except from a heatsink on the peltier element).
Peltier element work like fridges, they're cool on one side and hot on the other side when they get power. With a peltier element that's powerful enough, the processor could even be overclocked to run hundreds of MHz' above their rated speeds, with a fan to cool down the peltier element (the cooler they are on one side, the hotter they got on the other side).
Why does everybody do it so primitive, and put 3-6 fans in a computer, when they really only could have one fan and peltier elements/heatsinks?
Also, I think Apple should be selling Macs with a motherboard cooled down to -18°C, and the HD/optical drives could be in a seperate "room". I guess they would have no problem getting approval from Motorola to run G4s at 2x1.4 GHz or so in that temperature.
Back to the OS X on x86 thing, no, it won't happen, and there is no point in releasing OS X for x86. As mentioned earlier, Apple would have no way of optimalizing OS X for x86, either.