We have just 2 Windows PCs (2000 and XP), but we have 3 Mac OS X systems and one linux box. I spend so much more time keeping the Windows PCs running properly than all of the other computers together, and by a factor of 2 or 3.
Can you feel my frustration :-(
Really, the best computers are the OS X machines: everything works with minimal administration activities.
I think that the problem with Microsoft Windows is simply that marketing and adding new features is more important than producing stable, relatively secure software.