For a moderator your response is kind of stupid.
Windows is prevalent because its fairly stable and it works well.
US government uses it, hospitals use it, banks us it, engineering firms us it. Almost all US businesses use it regularly.
The only area where the Mac OS has more uses is in the design community.
In fact Windows 7 is significantly better than Windows XP and it runs very well on old hardware.
I have Win 7 installed on a 5 year old T60 Thinkpad,...