No, Windows is not a virus. Here's what viruses do:
1) They replicate quickly -- Okay, Windows does that.
2) Viruses use up valuable system resources, slowing down the system as they do so -- Okay, Windows does that.
3) Viruses will, from time to time, trash your hard disk -- Okay, Windows does that, too
4) Viruses are usually carried, unknown to the user, along with valuable programs and systems -- Sigh... Windows does that, too
5) Viruses will occasionally make the user suspect their system is too slow (see 2) and the user will buy new hardware -- Yup, that's with Windows, too
Until now it seems Windows is a virus but there are fundamental differences:
Viruses are well supported by their authors, are running on most systems, their program code is fast, compact and efficient and they tend to become more sophisticated as they mature.