Like I said I have tried running the game (several years ago) on my old PC that was with 128MB RAM, so if what you're saying is true, then how can I do this on my current PC? Is it possible to make it use less than 100MB of RAM? If it's not possible then what is the point of this discussion, you suggest that he should buy 20x PCs mega cheap PCs with 128MB RAM ?
Not even remotely, and I have no idea what would make you believe that was the intent. The intent was to give a proper estimation of what was required to run that many copies of WoW. Looking into two or three slave machines running 10-15 bots each will most likely yield the best results instead of one mega machine. As for forcing WoW to run at its absolute minimum requirement you would have to restrict its resource allotment. Running it at the bare minimum will force the game to chop and lag.
Now here's another question, does your current system do anything besides slave wow bots? If we are trying to create slave computers and not a machine he uses in between botting then we can also force other requirements to lower the minimum standards that will not affect him. You wouldn't do such a thing on a regular usage computer.