Remember the Intel version of NeXTStep? Even SCO Unix outsold it. ;)
The only X86 OS that has a prayer of beating MS is Linux, after that maybe *BSD. But Linux seems to be more popular.
P.S. I tried to download the 280M Darwin ISO image but I cannot get a complete download. Apple requires you to register with their "database" so that you comply with their open source license. Isn't this just a way to get a list of "potential" customers?