the mighty machine

If you want a high security then go for linux but most of the softwares game are not compalitable. Than comes Vista but vista is a complicated thing. So the bes one is Windows XP . Most of them use this Operating System.

I don't know what "Powerful" mean in an operating system But every system has its own capabilities i would recommend "mac os" as it is said to have the peak of graphics and the most advance security system

I think it depends on what your definition of most powerful one means...and I'm not exactly sure what you mean by "powerful" To the tech geeks, Linux is probably the most powerful OS simply because it is very customisable and very reliable...Some would say Mac OS... But most of us are Microsoft Windows users and among the released ones, Windows XP would be most reliable...